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diff --git a/Documentation/trace/coresight.txt b/Documentation/trace/coresight.txt
new file mode 100644
index 000000000..77d14d51a
--- /dev/null
+++ b/Documentation/trace/coresight.txt
@@ -0,0 +1,299 @@
+		Coresight - HW Assisted Tracing on ARM
+		======================================
+
+   Author:   Mathieu Poirier <mathieu.poirier@linaro.org>
+   Date:     September 11th, 2014
+
+Introduction
+------------
+
+Coresight is an umbrella of technologies allowing for the debugging of ARM
+based SoC.  It includes solutions for JTAG and HW assisted tracing.  This
+document is concerned with the latter.
+
+HW assisted tracing is becoming increasingly useful when dealing with systems
+that have many SoCs and other components like GPU and DMA engines.  ARM has
+developed a HW assisted tracing solution by means of different components, each
+being added to a design at synthesis time to cater to specific tracing needs.
+Compoments are generally categorised as source, link and sinks and are
+(usually) discovered using the AMBA bus.
+
+"Sources" generate a compressed stream representing the processor instruction
+path based on tracing scenarios as configured by users.  From there the stream
+flows through the coresight system (via ATB bus) using links that are connecting
+the emanating source to a sink(s).  Sinks serve as endpoints to the coresight
+implementation, either storing the compressed stream in a memory buffer or
+creating an interface to the outside world where data can be transferred to a
+host without fear of filling up the onboard coresight memory buffer.
+
+At typical coresight system would look like this:
+
+  *****************************************************************
+ **************************** AMBA AXI  ****************************===||
+  *****************************************************************    ||
+        ^                    ^                            |            ||
+        |                    |                            *            **
+     0000000    :::::     0000000    :::::    :::::    @@@@@@@    ||||||||||||
+     0 CPU 0<-->: C :     0 CPU 0<-->: C :    : C :    @ STM @    || System ||
+  |->0000000    : T :  |->0000000    : T :    : T :<--->@@@@@     || Memory ||
+  |  #######<-->: I :  |  #######<-->: I :    : I :      @@@<-|   ||||||||||||
+  |  # ETM #    :::::  |  # PTM #    :::::    :::::       @   |
+  |   #####      ^ ^   |   #####      ^ !      ^ !        .   |   |||||||||
+  | |->###       | !   | |->###       | !      | !        .   |   || DAP ||
+  | |   #        | !   | |   #        | !      | !        .   |   |||||||||
+  | |   .        | !   | |   .        | !      | !        .   |      |  |
+  | |   .        | !   | |   .        | !      | !        .   |      |  *
+  | |   .        | !   | |   .        | !      | !        .   |      | SWD/
+  | |   .        | !   | |   .        | !      | !        .   |      | JTAG
+  *****************************************************************<-|
+ *************************** AMBA Debug APB ************************
+  *****************************************************************
+   |    .          !         .          !        !        .    |
+   |    .          *         .          *        *        .    |
+  *****************************************************************
+ ******************** Cross Trigger Matrix (CTM) *******************
+  *****************************************************************
+   |    .     ^              .                            .    |
+   |    *     !              *                            *    |
+  *****************************************************************
+ ****************** AMBA Advanced Trace Bus (ATB) ******************
+  *****************************************************************
+   |          !                        ===============         |
+   |          *                         ===== F =====<---------|
+   |   :::::::::                         ==== U ====
+   |-->:: CTI ::<!!                       === N ===
+   |   :::::::::  !                        == N ==
+   |    ^         *                        == E ==
+   |    !  &&&&&&&&&       IIIIIII         == L ==
+   |------>&& ETB &&<......II     I        =======
+   |    !  &&&&&&&&&       II     I           .
+   |    !                    I     I          .
+   |    !                    I REP I<..........
+   |    !                    I     I
+   |    !!>&&&&&&&&&       II     I           *Source: ARM ltd.
+   |------>& TPIU  &<......II    I            DAP = Debug Access Port
+           &&&&&&&&&       IIIIIII            ETM = Embedded Trace Macrocell
+               ;                              PTM = Program Trace Macrocell
+               ;                              CTI = Cross Trigger Interface
+               *                              ETB = Embedded Trace Buffer
+          To trace port                       TPIU= Trace Port Interface Unit
+                                              SWD = Serial Wire Debug
+
+While on target configuration of the components is done via the APB bus,
+all trace data are carried out-of-band on the ATB bus.  The CTM provides
+a way to aggregate and distribute signals between CoreSight components.
+
+The coresight framework provides a central point to represent, configure and
+manage coresight devices on a platform.  This first implementation centers on
+the basic tracing functionality, enabling components such ETM/PTM, funnel,
+replicator, TMC, TPIU and ETB.  Future work will enable more
+intricate IP blocks such as STM and CTI.
+
+
+Acronyms and Classification
+---------------------------
+
+Acronyms:
+
+PTM:     Program Trace Macrocell
+ETM:     Embedded Trace Macrocell
+STM:     System trace Macrocell
+ETB:     Embedded Trace Buffer
+ITM:     Instrumentation Trace Macrocell
+TPIU:    Trace Port Interface Unit
+TMC-ETR: Trace Memory Controller, configured as Embedded Trace Router
+TMC-ETF: Trace Memory Controller, configured as Embedded Trace FIFO
+CTI:     Cross Trigger Interface
+
+Classification:
+
+Source:
+   ETMv3.x ETMv4, PTMv1.0, PTMv1.1, STM, STM500, ITM
+Link:
+   Funnel, replicator (intelligent or not), TMC-ETR
+Sinks:
+   ETBv1.0, ETB1.1, TPIU, TMC-ETF
+Misc:
+   CTI
+
+
+Device Tree Bindings
+----------------------
+
+See Documentation/devicetree/bindings/arm/coresight.txt for details.
+
+As of this writing drivers for ITM, STMs and CTIs are not provided but are
+expected to be added as the solution matures.
+
+
+Framework and implementation
+----------------------------
+
+The coresight framework provides a central point to represent, configure and
+manage coresight devices on a platform.  Any coresight compliant device can
+register with the framework for as long as they use the right APIs:
+
+struct coresight_device *coresight_register(struct coresight_desc *desc);
+void coresight_unregister(struct coresight_device *csdev);
+
+The registering function is taking a "struct coresight_device *csdev" and
+register the device with the core framework.  The unregister function takes
+a reference to a "strut coresight_device", obtained at registration time.
+
+If everything goes well during the registration process the new devices will
+show up under /sys/bus/coresight/devices, as showns here for a TC2 platform:
+
+root:~# ls /sys/bus/coresight/devices/
+replicator  20030000.tpiu    2201c000.ptm  2203c000.etm  2203e000.etm
+20010000.etb         20040000.funnel  2201d000.ptm  2203d000.etm
+root:~#
+
+The functions take a "struct coresight_device", which looks like this:
+
+struct coresight_desc {
+        enum coresight_dev_type type;
+        struct coresight_dev_subtype subtype;
+        const struct coresight_ops *ops;
+        struct coresight_platform_data *pdata;
+        struct device *dev;
+        const struct attribute_group **groups;
+};
+
+
+The "coresight_dev_type" identifies what the device is, i.e, source link or
+sink while the "coresight_dev_subtype" will characterise that type further.
+
+The "struct coresight_ops" is mandatory and will tell the framework how to
+perform base operations related to the components, each component having
+a different set of requirement.  For that "struct coresight_ops_sink",
+"struct coresight_ops_link" and "struct coresight_ops_source" have been
+provided.
+
+The next field, "struct coresight_platform_data *pdata" is acquired by calling
+"of_get_coresight_platform_data()", as part of the driver's _probe routine and
+"struct device *dev" gets the device reference embedded in the "amba_device":
+
+static int etm_probe(struct amba_device *adev, const struct amba_id *id)
+{
+ ...
+ ...
+ drvdata->dev = &adev->dev;
+ ...
+}
+
+Specific class of device (source, link, or sink) have generic operations
+that can be performed on them (see "struct coresight_ops").  The
+"**groups" is a list of sysfs entries pertaining to operations
+specific to that component only.  "Implementation defined" customisations are
+expected to be accessed and controlled using those entries.
+
+Last but not least, "struct module *owner" is expected to be set to reflect
+the information carried in "THIS_MODULE".
+
+How to use
+----------
+
+Before trace collection can start, a coresight sink needs to be identify.
+There is no limit on the amount of sinks (nor sources) that can be enabled at
+any given moment.  As a generic operation, all device pertaining to the sink
+class will have an "active" entry in sysfs:
+
+root:/sys/bus/coresight/devices# ls
+replicator  20030000.tpiu    2201c000.ptm  2203c000.etm  2203e000.etm
+20010000.etb         20040000.funnel  2201d000.ptm  2203d000.etm
+root:/sys/bus/coresight/devices# ls 20010000.etb
+enable_sink  status  trigger_cntr
+root:/sys/bus/coresight/devices# echo 1 > 20010000.etb/enable_sink
+root:/sys/bus/coresight/devices# cat 20010000.etb/enable_sink
+1
+root:/sys/bus/coresight/devices#
+
+At boot time the current etm3x driver will configure the first address
+comparator with "_stext" and "_etext", essentially tracing any instruction
+that falls within that range.  As such "enabling" a source will immediately
+trigger a trace capture:
+
+root:/sys/bus/coresight/devices# echo 1 > 2201c000.ptm/enable_source
+root:/sys/bus/coresight/devices# cat 2201c000.ptm/enable_source
+1
+root:/sys/bus/coresight/devices# cat 20010000.etb/status
+Depth:          0x2000
+Status:         0x1
+RAM read ptr:   0x0
+RAM wrt ptr:    0x19d3   <----- The write pointer is moving
+Trigger cnt:    0x0
+Control:        0x1
+Flush status:   0x0
+Flush ctrl:     0x2001
+root:/sys/bus/coresight/devices#
+
+Trace collection is stopped the same way:
+
+root:/sys/bus/coresight/devices# echo 0 > 2201c000.ptm/enable_source
+root:/sys/bus/coresight/devices#
+
+The content of the ETB buffer can be harvested directly from /dev:
+
+root:/sys/bus/coresight/devices# dd if=/dev/20010000.etb \
+of=~/cstrace.bin
+
+64+0 records in
+64+0 records out
+32768 bytes (33 kB) copied, 0.00125258 s, 26.2 MB/s
+root:/sys/bus/coresight/devices#
+
+The file cstrace.bin can be decompressed using "ptm2human", DS-5 or Trace32.
+
+Following is a DS-5 output of an experimental loop that increments a variable up
+to a certain value.  The example is simple and yet provides a glimpse of the
+wealth of possibilities that coresight provides.
+
+Info                                    Tracing enabled
+Instruction     106378866       0x8026B53C      E52DE004        false   PUSH     {lr}
+Instruction     0       0x8026B540      E24DD00C        false   SUB      sp,sp,#0xc
+Instruction     0       0x8026B544      E3A03000        false   MOV      r3,#0
+Instruction     0       0x8026B548      E58D3004        false   STR      r3,[sp,#4]
+Instruction     0       0x8026B54C      E59D3004        false   LDR      r3,[sp,#4]
+Instruction     0       0x8026B550      E3530004        false   CMP      r3,#4
+Instruction     0       0x8026B554      E2833001        false   ADD      r3,r3,#1
+Instruction     0       0x8026B558      E58D3004        false   STR      r3,[sp,#4]
+Instruction     0       0x8026B55C      DAFFFFFA        true    BLE      {pc}-0x10 ; 0x8026b54c
+Timestamp                                       Timestamp: 17106715833
+Instruction     319     0x8026B54C      E59D3004        false   LDR      r3,[sp,#4]
+Instruction     0       0x8026B550      E3530004        false   CMP      r3,#4
+Instruction     0       0x8026B554      E2833001        false   ADD      r3,r3,#1
+Instruction     0       0x8026B558      E58D3004        false   STR      r3,[sp,#4]
+Instruction     0       0x8026B55C      DAFFFFFA        true    BLE      {pc}-0x10 ; 0x8026b54c
+Instruction     9       0x8026B54C      E59D3004        false   LDR      r3,[sp,#4]
+Instruction     0       0x8026B550      E3530004        false   CMP      r3,#4
+Instruction     0       0x8026B554      E2833001        false   ADD      r3,r3,#1
+Instruction     0       0x8026B558      E58D3004        false   STR      r3,[sp,#4]
+Instruction     0       0x8026B55C      DAFFFFFA        true    BLE      {pc}-0x10 ; 0x8026b54c
+Instruction     7       0x8026B54C      E59D3004        false   LDR      r3,[sp,#4]
+Instruction     0       0x8026B550      E3530004        false   CMP      r3,#4
+Instruction     0       0x8026B554      E2833001        false   ADD      r3,r3,#1
+Instruction     0       0x8026B558      E58D3004        false   STR      r3,[sp,#4]
+Instruction     0       0x8026B55C      DAFFFFFA        true    BLE      {pc}-0x10 ; 0x8026b54c
+Instruction     7       0x8026B54C      E59D3004        false   LDR      r3,[sp,#4]
+Instruction     0       0x8026B550      E3530004        false   CMP      r3,#4
+Instruction     0       0x8026B554      E2833001        false   ADD      r3,r3,#1
+Instruction     0       0x8026B558      E58D3004        false   STR      r3,[sp,#4]
+Instruction     0       0x8026B55C      DAFFFFFA        true    BLE      {pc}-0x10 ; 0x8026b54c
+Instruction     10      0x8026B54C      E59D3004        false   LDR      r3,[sp,#4]
+Instruction     0       0x8026B550      E3530004        false   CMP      r3,#4
+Instruction     0       0x8026B554      E2833001        false   ADD      r3,r3,#1
+Instruction     0       0x8026B558      E58D3004        false   STR      r3,[sp,#4]
+Instruction     0       0x8026B55C      DAFFFFFA        true    BLE      {pc}-0x10 ; 0x8026b54c
+Instruction     6       0x8026B560      EE1D3F30        false   MRC      p15,#0x0,r3,c13,c0,#1
+Instruction     0       0x8026B564      E1A0100D        false   MOV      r1,sp
+Instruction     0       0x8026B568      E3C12D7F        false   BIC      r2,r1,#0x1fc0
+Instruction     0       0x8026B56C      E3C2203F        false   BIC      r2,r2,#0x3f
+Instruction     0       0x8026B570      E59D1004        false   LDR      r1,[sp,#4]
+Instruction     0       0x8026B574      E59F0010        false   LDR      r0,[pc,#16] ; [0x8026B58C] = 0x80550368
+Instruction     0       0x8026B578      E592200C        false   LDR      r2,[r2,#0xc]
+Instruction     0       0x8026B57C      E59221D0        false   LDR      r2,[r2,#0x1d0]
+Instruction     0       0x8026B580      EB07A4CF        true    BL       {pc}+0x1e9344 ; 0x804548c4
+Info                                    Tracing enabled
+Instruction     13570831        0x8026B584      E28DD00C        false   ADD      sp,sp,#0xc
+Instruction     0       0x8026B588      E8BD8000        true    LDM      sp!,{pc}
+Timestamp                                       Timestamp: 17107041535
diff --git a/Documentation/trace/events-kmem.txt b/Documentation/trace/events-kmem.txt
new file mode 100644
index 000000000..194800410
--- /dev/null
+++ b/Documentation/trace/events-kmem.txt
@@ -0,0 +1,107 @@
+			Subsystem Trace Points: kmem
+
+The kmem tracing system captures events related to object and page allocation
+within the kernel. Broadly speaking there are five major subheadings.
+
+  o Slab allocation of small objects of unknown type (kmalloc)
+  o Slab allocation of small objects of known type
+  o Page allocation
+  o Per-CPU Allocator Activity
+  o External Fragmentation
+
+This document describes what each of the tracepoints is and why they
+might be useful.
+
+1. Slab allocation of small objects of unknown type
+===================================================
+kmalloc		call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s
+kmalloc_node	call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s node=%d
+kfree		call_site=%lx ptr=%p
+
+Heavy activity for these events may indicate that a specific cache is
+justified, particularly if kmalloc slab pages are getting significantly
+internal fragmented as a result of the allocation pattern. By correlating
+kmalloc with kfree, it may be possible to identify memory leaks and where
+the allocation sites were.
+
+
+2. Slab allocation of small objects of known type
+=================================================
+kmem_cache_alloc	call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s
+kmem_cache_alloc_node	call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s node=%d
+kmem_cache_free		call_site=%lx ptr=%p
+
+These events are similar in usage to the kmalloc-related events except that
+it is likely easier to pin the event down to a specific cache. At the time
+of writing, no information is available on what slab is being allocated from,
+but the call_site can usually be used to extrapolate that information.
+
+3. Page allocation
+==================
+mm_page_alloc		  page=%p pfn=%lu order=%d migratetype=%d gfp_flags=%s
+mm_page_alloc_zone_locked page=%p pfn=%lu order=%u migratetype=%d cpu=%d percpu_refill=%d
+mm_page_free		  page=%p pfn=%lu order=%d
+mm_page_free_batched	  page=%p pfn=%lu order=%d cold=%d
+
+These four events deal with page allocation and freeing. mm_page_alloc is
+a simple indicator of page allocator activity. Pages may be allocated from
+the per-CPU allocator (high performance) or the buddy allocator.
+
+If pages are allocated directly from the buddy allocator, the
+mm_page_alloc_zone_locked event is triggered. This event is important as high
+amounts of activity imply high activity on the zone->lock. Taking this lock
+impairs performance by disabling interrupts, dirtying cache lines between
+CPUs and serialising many CPUs.
+
+When a page is freed directly by the caller, the only mm_page_free event
+is triggered. Significant amounts of activity here could indicate that the
+callers should be batching their activities.
+
+When pages are freed in batch, the also mm_page_free_batched is triggered.
+Broadly speaking, pages are taken off the LRU lock in bulk and
+freed in batch with a page list. Significant amounts of activity here could
+indicate that the system is under memory pressure and can also indicate
+contention on the zone->lru_lock.
+
+4. Per-CPU Allocator Activity
+=============================
+mm_page_alloc_zone_locked	page=%p pfn=%lu order=%u migratetype=%d cpu=%d percpu_refill=%d
+mm_page_pcpu_drain		page=%p pfn=%lu order=%d cpu=%d migratetype=%d
+
+In front of the page allocator is a per-cpu page allocator. It exists only
+for order-0 pages, reduces contention on the zone->lock and reduces the
+amount of writing on struct page.
+
+When a per-CPU list is empty or pages of the wrong type are allocated,
+the zone->lock will be taken once and the per-CPU list refilled. The event
+triggered is mm_page_alloc_zone_locked for each page allocated with the
+event indicating whether it is for a percpu_refill or not.
+
+When the per-CPU list is too full, a number of pages are freed, each one
+which triggers a mm_page_pcpu_drain event.
+
+The individual nature of the events is so that pages can be tracked
+between allocation and freeing. A number of drain or refill pages that occur
+consecutively imply the zone->lock being taken once. Large amounts of per-CPU
+refills and drains could imply an imbalance between CPUs where too much work
+is being concentrated in one place. It could also indicate that the per-CPU
+lists should be a larger size. Finally, large amounts of refills on one CPU
+and drains on another could be a factor in causing large amounts of cache
+line bounces due to writes between CPUs and worth investigating if pages
+can be allocated and freed on the same CPU through some algorithm change.
+
+5. External Fragmentation
+=========================
+mm_page_alloc_extfrag		page=%p pfn=%lu alloc_order=%d fallback_order=%d pageblock_order=%d alloc_migratetype=%d fallback_migratetype=%d fragmenting=%d change_ownership=%d
+
+External fragmentation affects whether a high-order allocation will be
+successful or not. For some types of hardware, this is important although
+it is avoided where possible. If the system is using huge pages and needs
+to be able to resize the pool over the lifetime of the system, this value
+is important.
+
+Large numbers of this event implies that memory is fragmenting and
+high-order allocations will start failing at some time in the future. One
+means of reducing the occurrence of this event is to increase the size of
+min_free_kbytes in increments of 3*pageblock_size*nr_online_nodes where
+pageblock_size is usually the size of the default hugepage size.
diff --git a/Documentation/trace/events-nmi.txt b/Documentation/trace/events-nmi.txt
new file mode 100644
index 000000000..c03c8c89f
--- /dev/null
+++ b/Documentation/trace/events-nmi.txt
@@ -0,0 +1,43 @@
+NMI Trace Events
+
+These events normally show up here:
+
+	/sys/kernel/debug/tracing/events/nmi
+
+--
+
+nmi_handler:
+
+You might want to use this tracepoint if you suspect that your
+NMI handlers are hogging large amounts of CPU time.  The kernel
+will warn if it sees long-running handlers:
+
+	INFO: NMI handler took too long to run: 9.207 msecs
+
+and this tracepoint will allow you to drill down and get some
+more details.
+
+Let's say you suspect that perf_event_nmi_handler() is causing
+you some problems and you only want to trace that handler
+specifically.  You need to find its address:
+
+	$ grep perf_event_nmi_handler /proc/kallsyms
+	ffffffff81625600 t perf_event_nmi_handler
+
+Let's also say you are only interested in when that function is
+really hogging a lot of CPU time, like a millisecond at a time.
+Note that the kernel's output is in milliseconds, but the input
+to the filter is in nanoseconds!  You can filter on 'delta_ns':
+
+cd /sys/kernel/debug/tracing/events/nmi/nmi_handler
+echo 'handler==0xffffffff81625600 && delta_ns>1000000' > filter
+echo 1 > enable
+
+Your output would then look like:
+
+$ cat /sys/kernel/debug/tracing/trace_pipe
+<idle>-0     [000] d.h3   505.397558: nmi_handler: perf_event_nmi_handler() delta_ns: 3236765 handled: 1
+<idle>-0     [000] d.h3   505.805893: nmi_handler: perf_event_nmi_handler() delta_ns: 3174234 handled: 1
+<idle>-0     [000] d.h3   506.158206: nmi_handler: perf_event_nmi_handler() delta_ns: 3084642 handled: 1
+<idle>-0     [000] d.h3   506.334346: nmi_handler: perf_event_nmi_handler() delta_ns: 3080351 handled: 1
+
diff --git a/Documentation/trace/events-power.txt b/Documentation/trace/events-power.txt
new file mode 100644
index 000000000..21d514ced
--- /dev/null
+++ b/Documentation/trace/events-power.txt
@@ -0,0 +1,96 @@
+
+			Subsystem Trace Points: power
+
+The power tracing system captures events related to power transitions
+within the kernel. Broadly speaking there are three major subheadings:
+
+  o Power state switch which reports events related to suspend (S-states),
+     cpuidle (C-states) and cpufreq (P-states)
+  o System clock related changes
+  o Power domains related changes and transitions
+
+This document describes what each of the tracepoints is and why they
+might be useful.
+
+Cf. include/trace/events/power.h for the events definitions.
+
+1. Power state switch events
+============================
+
+1.1 Trace API
+-----------------
+
+A 'cpu' event class gathers the CPU-related events: cpuidle and
+cpufreq.
+
+cpu_idle		"state=%lu cpu_id=%lu"
+cpu_frequency		"state=%lu cpu_id=%lu"
+
+A suspend event is used to indicate the system going in and out of the
+suspend mode:
+
+machine_suspend		"state=%lu"
+
+
+Note: the value of '-1' or '4294967295' for state means an exit from the current state,
+i.e. trace_cpu_idle(4, smp_processor_id()) means that the system
+enters the idle state 4, while trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id())
+means that the system exits the previous idle state.
+
+The event which has 'state=4294967295' in the trace is very important to the user
+space tools which are using it to detect the end of the current state, and so to
+correctly draw the states diagrams and to calculate accurate statistics etc.
+
+2. Clocks events
+================
+The clock events are used for clock enable/disable and for
+clock rate change.
+
+clock_enable		"%s state=%lu cpu_id=%lu"
+clock_disable		"%s state=%lu cpu_id=%lu"
+clock_set_rate		"%s state=%lu cpu_id=%lu"
+
+The first parameter gives the clock name (e.g. "gpio1_iclk").
+The second parameter is '1' for enable, '0' for disable, the target
+clock rate for set_rate.
+
+3. Power domains events
+=======================
+The power domain events are used for power domains transitions
+
+power_domain_target	"%s state=%lu cpu_id=%lu"
+
+The first parameter gives the power domain name (e.g. "mpu_pwrdm").
+The second parameter is the power domain target state.
+
+4. PM QoS events
+================
+The PM QoS events are used for QoS add/update/remove request and for
+target/flags update.
+
+pm_qos_add_request                 "pm_qos_class=%s value=%d"
+pm_qos_update_request              "pm_qos_class=%s value=%d"
+pm_qos_remove_request              "pm_qos_class=%s value=%d"
+pm_qos_update_request_timeout      "pm_qos_class=%s value=%d, timeout_us=%ld"
+
+The first parameter gives the QoS class name (e.g. "CPU_DMA_LATENCY").
+The second parameter is value to be added/updated/removed.
+The third parameter is timeout value in usec.
+
+pm_qos_update_target               "action=%s prev_value=%d curr_value=%d"
+pm_qos_update_flags                "action=%s prev_value=0x%x curr_value=0x%x"
+
+The first parameter gives the QoS action name (e.g. "ADD_REQ").
+The second parameter is the previous QoS value.
+The third parameter is the current QoS value to update.
+
+And, there are also events used for device PM QoS add/update/remove request.
+
+dev_pm_qos_add_request             "device=%s type=%s new_value=%d"
+dev_pm_qos_update_request          "device=%s type=%s new_value=%d"
+dev_pm_qos_remove_request          "device=%s type=%s new_value=%d"
+
+The first parameter gives the device name which tries to add/update/remove
+QoS requests.
+The second parameter gives the request type (e.g. "DEV_PM_QOS_RESUME_LATENCY").
+The third parameter is value to be added/updated/removed.
diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt
new file mode 100644
index 000000000..75d25a1d6
--- /dev/null
+++ b/Documentation/trace/events.txt
@@ -0,0 +1,496 @@
+			     Event Tracing
+
+		Documentation written by Theodore Ts'o
+		Updated by Li Zefan and Tom Zanussi
+
+1. Introduction
+===============
+
+Tracepoints (see Documentation/trace/tracepoints.txt) can be used
+without creating custom kernel modules to register probe functions
+using the event tracing infrastructure.
+
+Not all tracepoints can be traced using the event tracing system;
+the kernel developer must provide code snippets which define how the
+tracing information is saved into the tracing buffer, and how the
+tracing information should be printed.
+
+2. Using Event Tracing
+======================
+
+2.1 Via the 'set_event' interface
+---------------------------------
+
+The events which are available for tracing can be found in the file
+/sys/kernel/debug/tracing/available_events.
+
+To enable a particular event, such as 'sched_wakeup', simply echo it
+to /sys/kernel/debug/tracing/set_event. For example:
+
+	# echo sched_wakeup >> /sys/kernel/debug/tracing/set_event
+
+[ Note: '>>' is necessary, otherwise it will firstly disable
+  all the events. ]
+
+To disable an event, echo the event name to the set_event file prefixed
+with an exclamation point:
+
+	# echo '!sched_wakeup' >> /sys/kernel/debug/tracing/set_event
+
+To disable all events, echo an empty line to the set_event file:
+
+	# echo > /sys/kernel/debug/tracing/set_event
+
+To enable all events, echo '*:*' or '*:' to the set_event file:
+
+	# echo *:* > /sys/kernel/debug/tracing/set_event
+
+The events are organized into subsystems, such as ext4, irq, sched,
+etc., and a full event name looks like this: <subsystem>:<event>.  The
+subsystem name is optional, but it is displayed in the available_events
+file.  All of the events in a subsystem can be specified via the syntax
+"<subsystem>:*"; for example, to enable all irq events, you can use the
+command:
+
+	# echo 'irq:*' > /sys/kernel/debug/tracing/set_event
+
+2.2 Via the 'enable' toggle
+---------------------------
+
+The events available are also listed in /sys/kernel/debug/tracing/events/ hierarchy
+of directories.
+
+To enable event 'sched_wakeup':
+
+	# echo 1 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable
+
+To disable it:
+
+	# echo 0 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable
+
+To enable all events in sched subsystem:
+
+	# echo 1 > /sys/kernel/debug/tracing/events/sched/enable
+
+To enable all events:
+
+	# echo 1 > /sys/kernel/debug/tracing/events/enable
+
+When reading one of these enable files, there are four results:
+
+ 0 - all events this file affects are disabled
+ 1 - all events this file affects are enabled
+ X - there is a mixture of events enabled and disabled
+ ? - this file does not affect any event
+
+2.3 Boot option
+---------------
+
+In order to facilitate early boot debugging, use boot option:
+
+	trace_event=[event-list]
+
+event-list is a comma separated list of events. See section 2.1 for event
+format.
+
+3. Defining an event-enabled tracepoint
+=======================================
+
+See The example provided in samples/trace_events
+
+4. Event formats
+================
+
+Each trace event has a 'format' file associated with it that contains
+a description of each field in a logged event.  This information can
+be used to parse the binary trace stream, and is also the place to
+find the field names that can be used in event filters (see section 5).
+
+It also displays the format string that will be used to print the
+event in text mode, along with the event name and ID used for
+profiling.
+
+Every event has a set of 'common' fields associated with it; these are
+the fields prefixed with 'common_'.  The other fields vary between
+events and correspond to the fields defined in the TRACE_EVENT
+definition for that event.
+
+Each field in the format has the form:
+
+     field:field-type field-name; offset:N; size:N;
+
+where offset is the offset of the field in the trace record and size
+is the size of the data item, in bytes.
+
+For example, here's the information displayed for the 'sched_wakeup'
+event:
+
+# cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/format
+
+name: sched_wakeup
+ID: 60
+format:
+	field:unsigned short common_type;	offset:0;	size:2;
+	field:unsigned char common_flags;	offset:2;	size:1;
+	field:unsigned char common_preempt_count;	offset:3;	size:1;
+	field:int common_pid;	offset:4;	size:4;
+	field:int common_tgid;	offset:8;	size:4;
+
+	field:char comm[TASK_COMM_LEN];	offset:12;	size:16;
+	field:pid_t pid;	offset:28;	size:4;
+	field:int prio;	offset:32;	size:4;
+	field:int success;	offset:36;	size:4;
+	field:int cpu;	offset:40;	size:4;
+
+print fmt: "task %s:%d [%d] success=%d [%03d]", REC->comm, REC->pid,
+	   REC->prio, REC->success, REC->cpu
+
+This event contains 10 fields, the first 5 common and the remaining 5
+event-specific.  All the fields for this event are numeric, except for
+'comm' which is a string, a distinction important for event filtering.
+
+5. Event filtering
+==================
+
+Trace events can be filtered in the kernel by associating boolean
+'filter expressions' with them.  As soon as an event is logged into
+the trace buffer, its fields are checked against the filter expression
+associated with that event type.  An event with field values that
+'match' the filter will appear in the trace output, and an event whose
+values don't match will be discarded.  An event with no filter
+associated with it matches everything, and is the default when no
+filter has been set for an event.
+
+5.1 Expression syntax
+---------------------
+
+A filter expression consists of one or more 'predicates' that can be
+combined using the logical operators '&&' and '||'.  A predicate is
+simply a clause that compares the value of a field contained within a
+logged event with a constant value and returns either 0 or 1 depending
+on whether the field value matched (1) or didn't match (0):
+
+	  field-name relational-operator value
+
+Parentheses can be used to provide arbitrary logical groupings and
+double-quotes can be used to prevent the shell from interpreting
+operators as shell metacharacters.
+
+The field-names available for use in filters can be found in the
+'format' files for trace events (see section 4).
+
+The relational-operators depend on the type of the field being tested:
+
+The operators available for numeric fields are:
+
+==, !=, <, <=, >, >=, &
+
+And for string fields they are:
+
+==, !=, ~
+
+The glob (~) only accepts a wild card character (*) at the start and or
+end of the string. For example:
+
+  prev_comm ~ "*sh"
+  prev_comm ~ "sh*"
+  prev_comm ~ "*sh*"
+
+But does not allow for it to be within the string:
+
+  prev_comm ~ "ba*sh"   <-- is invalid
+
+5.2 Setting filters
+-------------------
+
+A filter for an individual event is set by writing a filter expression
+to the 'filter' file for the given event.
+
+For example:
+
+# cd /sys/kernel/debug/tracing/events/sched/sched_wakeup
+# echo "common_preempt_count > 4" > filter
+
+A slightly more involved example:
+
+# cd /sys/kernel/debug/tracing/events/signal/signal_generate
+# echo "((sig >= 10 && sig < 15) || sig == 17) && comm != bash" > filter
+
+If there is an error in the expression, you'll get an 'Invalid
+argument' error when setting it, and the erroneous string along with
+an error message can be seen by looking at the filter e.g.:
+
+# cd /sys/kernel/debug/tracing/events/signal/signal_generate
+# echo "((sig >= 10 && sig < 15) || dsig == 17) && comm != bash" > filter
+-bash: echo: write error: Invalid argument
+# cat filter
+((sig >= 10 && sig < 15) || dsig == 17) && comm != bash
+^
+parse_error: Field not found
+
+Currently the caret ('^') for an error always appears at the beginning of
+the filter string; the error message should still be useful though
+even without more accurate position info.
+
+5.3 Clearing filters
+--------------------
+
+To clear the filter for an event, write a '0' to the event's filter
+file.
+
+To clear the filters for all events in a subsystem, write a '0' to the
+subsystem's filter file.
+
+5.3 Subsystem filters
+---------------------
+
+For convenience, filters for every event in a subsystem can be set or
+cleared as a group by writing a filter expression into the filter file
+at the root of the subsystem.  Note however, that if a filter for any
+event within the subsystem lacks a field specified in the subsystem
+filter, or if the filter can't be applied for any other reason, the
+filter for that event will retain its previous setting.  This can
+result in an unintended mixture of filters which could lead to
+confusing (to the user who might think different filters are in
+effect) trace output.  Only filters that reference just the common
+fields can be guaranteed to propagate successfully to all events.
+
+Here are a few subsystem filter examples that also illustrate the
+above points:
+
+Clear the filters on all events in the sched subsystem:
+
+# cd /sys/kernel/debug/tracing/events/sched
+# echo 0 > filter
+# cat sched_switch/filter
+none
+# cat sched_wakeup/filter
+none
+
+Set a filter using only common fields for all events in the sched
+subsystem (all events end up with the same filter):
+
+# cd /sys/kernel/debug/tracing/events/sched
+# echo common_pid == 0 > filter
+# cat sched_switch/filter
+common_pid == 0
+# cat sched_wakeup/filter
+common_pid == 0
+
+Attempt to set a filter using a non-common field for all events in the
+sched subsystem (all events but those that have a prev_pid field retain
+their old filters):
+
+# cd /sys/kernel/debug/tracing/events/sched
+# echo prev_pid == 0 > filter
+# cat sched_switch/filter
+prev_pid == 0
+# cat sched_wakeup/filter
+common_pid == 0
+
+6. Event triggers
+=================
+
+Trace events can be made to conditionally invoke trigger 'commands'
+which can take various forms and are described in detail below;
+examples would be enabling or disabling other trace events or invoking
+a stack trace whenever the trace event is hit.  Whenever a trace event
+with attached triggers is invoked, the set of trigger commands
+associated with that event is invoked.  Any given trigger can
+additionally have an event filter of the same form as described in
+section 5 (Event filtering) associated with it - the command will only
+be invoked if the event being invoked passes the associated filter.
+If no filter is associated with the trigger, it always passes.
+
+Triggers are added to and removed from a particular event by writing
+trigger expressions to the 'trigger' file for the given event.
+
+A given event can have any number of triggers associated with it,
+subject to any restrictions that individual commands may have in that
+regard.
+
+Event triggers are implemented on top of "soft" mode, which means that
+whenever a trace event has one or more triggers associated with it,
+the event is activated even if it isn't actually enabled, but is
+disabled in a "soft" mode.  That is, the tracepoint will be called,
+but just will not be traced, unless of course it's actually enabled.
+This scheme allows triggers to be invoked even for events that aren't
+enabled, and also allows the current event filter implementation to be
+used for conditionally invoking triggers.
+
+The syntax for event triggers is roughly based on the syntax for
+set_ftrace_filter 'ftrace filter commands' (see the 'Filter commands'
+section of Documentation/trace/ftrace.txt), but there are major
+differences and the implementation isn't currently tied to it in any
+way, so beware about making generalizations between the two.
+
+6.1 Expression syntax
+---------------------
+
+Triggers are added by echoing the command to the 'trigger' file:
+
+  # echo 'command[:count] [if filter]' > trigger
+
+Triggers are removed by echoing the same command but starting with '!'
+to the 'trigger' file:
+
+  # echo '!command[:count] [if filter]' > trigger
+
+The [if filter] part isn't used in matching commands when removing, so
+leaving that off in a '!' command will accomplish the same thing as
+having it in.
+
+The filter syntax is the same as that described in the 'Event
+filtering' section above.
+
+For ease of use, writing to the trigger file using '>' currently just
+adds or removes a single trigger and there's no explicit '>>' support
+('>' actually behaves like '>>') or truncation support to remove all
+triggers (you have to use '!' for each one added.)
+
+6.2 Supported trigger commands
+------------------------------
+
+The following commands are supported:
+
+- enable_event/disable_event
+
+  These commands can enable or disable another trace event whenever
+  the triggering event is hit.  When these commands are registered,
+  the other trace event is activated, but disabled in a "soft" mode.
+  That is, the tracepoint will be called, but just will not be traced.
+  The event tracepoint stays in this mode as long as there's a trigger
+  in effect that can trigger it.
+
+  For example, the following trigger causes kmalloc events to be
+  traced when a read system call is entered, and the :1 at the end
+  specifies that this enablement happens only once:
+
+  # echo 'enable_event:kmem:kmalloc:1' > \
+      /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
+
+  The following trigger causes kmalloc events to stop being traced
+  when a read system call exits.  This disablement happens on every
+  read system call exit:
+
+  # echo 'disable_event:kmem:kmalloc' > \
+      /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger
+
+  The format is:
+
+      enable_event:<system>:<event>[:count]
+      disable_event:<system>:<event>[:count]
+
+  To remove the above commands:
+
+  # echo '!enable_event:kmem:kmalloc:1' > \
+      /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
+
+  # echo '!disable_event:kmem:kmalloc' > \
+      /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger
+
+  Note that there can be any number of enable/disable_event triggers
+  per triggering event, but there can only be one trigger per
+  triggered event. e.g. sys_enter_read can have triggers enabling both
+  kmem:kmalloc and sched:sched_switch, but can't have two kmem:kmalloc
+  versions such as kmem:kmalloc and kmem:kmalloc:1 or 'kmem:kmalloc if
+  bytes_req == 256' and 'kmem:kmalloc if bytes_alloc == 256' (they
+  could be combined into a single filter on kmem:kmalloc though).
+
+- stacktrace
+
+  This command dumps a stacktrace in the trace buffer whenever the
+  triggering event occurs.
+
+  For example, the following trigger dumps a stacktrace every time the
+  kmalloc tracepoint is hit:
+
+  # echo 'stacktrace' > \
+        /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+  The following trigger dumps a stacktrace the first 5 times a kmalloc
+  request happens with a size >= 64K
+
+  # echo 'stacktrace:5 if bytes_req >= 65536' > \
+        /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+  The format is:
+
+      stacktrace[:count]
+
+  To remove the above commands:
+
+  # echo '!stacktrace' > \
+        /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+  # echo '!stacktrace:5 if bytes_req >= 65536' > \
+        /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+  The latter can also be removed more simply by the following (without
+  the filter):
+
+  # echo '!stacktrace:5' > \
+        /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+  Note that there can be only one stacktrace trigger per triggering
+  event.
+
+- snapshot
+
+  This command causes a snapshot to be triggered whenever the
+  triggering event occurs.
+
+  The following command creates a snapshot every time a block request
+  queue is unplugged with a depth > 1.  If you were tracing a set of
+  events or functions at the time, the snapshot trace buffer would
+  capture those events when the trigger event occurred:
+
+  # echo 'snapshot if nr_rq > 1' > \
+        /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+  To only snapshot once:
+
+  # echo 'snapshot:1 if nr_rq > 1' > \
+        /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+  To remove the above commands:
+
+  # echo '!snapshot if nr_rq > 1' > \
+        /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+  # echo '!snapshot:1 if nr_rq > 1' > \
+        /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+  Note that there can be only one snapshot trigger per triggering
+  event.
+
+- traceon/traceoff
+
+  These commands turn tracing on and off when the specified events are
+  hit. The parameter determines how many times the tracing system is
+  turned on and off. If unspecified, there is no limit.
+
+  The following command turns tracing off the first time a block
+  request queue is unplugged with a depth > 1.  If you were tracing a
+  set of events or functions at the time, you could then examine the
+  trace buffer to see the sequence of events that led up to the
+  trigger event:
+
+  # echo 'traceoff:1 if nr_rq > 1' > \
+        /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+  To always disable tracing when nr_rq  > 1 :
+
+  # echo 'traceoff if nr_rq > 1' > \
+        /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+  To remove the above commands:
+
+  # echo '!traceoff:1 if nr_rq > 1' > \
+        /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+  # echo '!traceoff if nr_rq > 1' > \
+        /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+  Note that there can be only one traceon or traceoff trigger per
+  triggering event.
diff --git a/Documentation/trace/ftrace-design.txt b/Documentation/trace/ftrace-design.txt
new file mode 100644
index 000000000..dd5f916b3
--- /dev/null
+++ b/Documentation/trace/ftrace-design.txt
@@ -0,0 +1,382 @@
+		function tracer guts
+		====================
+		By Mike Frysinger
+
+Introduction
+------------
+
+Here we will cover the architecture pieces that the common function tracing
+code relies on for proper functioning.  Things are broken down into increasing
+complexity so that you can start simple and at least get basic functionality.
+
+Note that this focuses on architecture implementation details only.  If you
+want more explanation of a feature in terms of common code, review the common
+ftrace.txt file.
+
+Ideally, everyone who wishes to retain performance while supporting tracing in
+their kernel should make it all the way to dynamic ftrace support.
+
+
+Prerequisites
+-------------
+
+Ftrace relies on these features being implemented:
+ STACKTRACE_SUPPORT - implement save_stack_trace()
+ TRACE_IRQFLAGS_SUPPORT - implement include/asm/irqflags.h
+
+
+HAVE_FUNCTION_TRACER
+--------------------
+
+You will need to implement the mcount and the ftrace_stub functions.
+
+The exact mcount symbol name will depend on your toolchain.  Some call it
+"mcount", "_mcount", or even "__mcount".  You can probably figure it out by
+running something like:
+	$ echo 'main(){}' | gcc -x c -S -o - - -pg | grep mcount
+	        call    mcount
+We'll make the assumption below that the symbol is "mcount" just to keep things
+nice and simple in the examples.
+
+Keep in mind that the ABI that is in effect inside of the mcount function is
+*highly* architecture/toolchain specific.  We cannot help you in this regard,
+sorry.  Dig up some old documentation and/or find someone more familiar than
+you to bang ideas off of.  Typically, register usage (argument/scratch/etc...)
+is a major issue at this point, especially in relation to the location of the
+mcount call (before/after function prologue).  You might also want to look at
+how glibc has implemented the mcount function for your architecture.  It might
+be (semi-)relevant.
+
+The mcount function should check the function pointer ftrace_trace_function
+to see if it is set to ftrace_stub.  If it is, there is nothing for you to do,
+so return immediately.  If it isn't, then call that function in the same way
+the mcount function normally calls __mcount_internal -- the first argument is
+the "frompc" while the second argument is the "selfpc" (adjusted to remove the
+size of the mcount call that is embedded in the function).
+
+For example, if the function foo() calls bar(), when the bar() function calls
+mcount(), the arguments mcount() will pass to the tracer are:
+	"frompc" - the address bar() will use to return to foo()
+	"selfpc" - the address bar() (with mcount() size adjustment)
+
+Also keep in mind that this mcount function will be called *a lot*, so
+optimizing for the default case of no tracer will help the smooth running of
+your system when tracing is disabled.  So the start of the mcount function is
+typically the bare minimum with checking things before returning.  That also
+means the code flow should usually be kept linear (i.e. no branching in the nop
+case).  This is of course an optimization and not a hard requirement.
+
+Here is some pseudo code that should help (these functions should actually be
+implemented in assembly):
+
+void ftrace_stub(void)
+{
+	return;
+}
+
+void mcount(void)
+{
+	/* save any bare state needed in order to do initial checking */
+
+	extern void (*ftrace_trace_function)(unsigned long, unsigned long);
+	if (ftrace_trace_function != ftrace_stub)
+		goto do_trace;
+
+	/* restore any bare state */
+
+	return;
+
+do_trace:
+
+	/* save all state needed by the ABI (see paragraph above) */
+
+	unsigned long frompc = ...;
+	unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE;
+	ftrace_trace_function(frompc, selfpc);
+
+	/* restore all state needed by the ABI */
+}
+
+Don't forget to export mcount for modules !
+extern void mcount(void);
+EXPORT_SYMBOL(mcount);
+
+
+HAVE_FUNCTION_GRAPH_TRACER
+--------------------------
+
+Deep breath ... time to do some real work.  Here you will need to update the
+mcount function to check ftrace graph function pointers, as well as implement
+some functions to save (hijack) and restore the return address.
+
+The mcount function should check the function pointers ftrace_graph_return
+(compare to ftrace_stub) and ftrace_graph_entry (compare to
+ftrace_graph_entry_stub).  If either of those is not set to the relevant stub
+function, call the arch-specific function ftrace_graph_caller which in turn
+calls the arch-specific function prepare_ftrace_return.  Neither of these
+function names is strictly required, but you should use them anyway to stay
+consistent across the architecture ports -- easier to compare & contrast
+things.
+
+The arguments to prepare_ftrace_return are slightly different than what are
+passed to ftrace_trace_function.  The second argument "selfpc" is the same,
+but the first argument should be a pointer to the "frompc".  Typically this is
+located on the stack.  This allows the function to hijack the return address
+temporarily to have it point to the arch-specific function return_to_handler.
+That function will simply call the common ftrace_return_to_handler function and
+that will return the original return address with which you can return to the
+original call site.
+
+Here is the updated mcount pseudo code:
+void mcount(void)
+{
+...
+	if (ftrace_trace_function != ftrace_stub)
+		goto do_trace;
+
++#ifdef CONFIG_FUNCTION_GRAPH_TRACER
++	extern void (*ftrace_graph_return)(...);
++	extern void (*ftrace_graph_entry)(...);
++	if (ftrace_graph_return != ftrace_stub ||
++	    ftrace_graph_entry != ftrace_graph_entry_stub)
++		ftrace_graph_caller();
++#endif
+
+	/* restore any bare state */
+...
+
+Here is the pseudo code for the new ftrace_graph_caller assembly function:
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+void ftrace_graph_caller(void)
+{
+	/* save all state needed by the ABI */
+
+	unsigned long *frompc = &...;
+	unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE;
+	/* passing frame pointer up is optional -- see below */
+	prepare_ftrace_return(frompc, selfpc, frame_pointer);
+
+	/* restore all state needed by the ABI */
+}
+#endif
+
+For information on how to implement prepare_ftrace_return(), simply look at the
+x86 version (the frame pointer passing is optional; see the next section for
+more information).  The only architecture-specific piece in it is the setup of
+the fault recovery table (the asm(...) code).  The rest should be the same
+across architectures.
+
+Here is the pseudo code for the new return_to_handler assembly function.  Note
+that the ABI that applies here is different from what applies to the mcount
+code.  Since you are returning from a function (after the epilogue), you might
+be able to skimp on things saved/restored (usually just registers used to pass
+return values).
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+void return_to_handler(void)
+{
+	/* save all state needed by the ABI (see paragraph above) */
+
+	void (*original_return_point)(void) = ftrace_return_to_handler();
+
+	/* restore all state needed by the ABI */
+
+	/* this is usually either a return or a jump */
+	original_return_point();
+}
+#endif
+
+
+HAVE_FUNCTION_GRAPH_FP_TEST
+---------------------------
+
+An arch may pass in a unique value (frame pointer) to both the entering and
+exiting of a function.  On exit, the value is compared and if it does not
+match, then it will panic the kernel.  This is largely a sanity check for bad
+code generation with gcc.  If gcc for your port sanely updates the frame
+pointer under different optimization levels, then ignore this option.
+
+However, adding support for it isn't terribly difficult.  In your assembly code
+that calls prepare_ftrace_return(), pass the frame pointer as the 3rd argument.
+Then in the C version of that function, do what the x86 port does and pass it
+along to ftrace_push_return_trace() instead of a stub value of 0.
+
+Similarly, when you call ftrace_return_to_handler(), pass it the frame pointer.
+
+
+HAVE_FTRACE_NMI_ENTER
+---------------------
+
+If you can't trace NMI functions, then skip this option.
+
+<details to be filled>
+
+
+HAVE_SYSCALL_TRACEPOINTS
+------------------------
+
+You need very few things to get the syscalls tracing in an arch.
+
+- Support HAVE_ARCH_TRACEHOOK (see arch/Kconfig).
+- Have a NR_syscalls variable in <asm/unistd.h> that provides the number
+  of syscalls supported by the arch.
+- Support the TIF_SYSCALL_TRACEPOINT thread flags.
+- Put the trace_sys_enter() and trace_sys_exit() tracepoints calls from ptrace
+  in the ptrace syscalls tracing path.
+- If the system call table on this arch is more complicated than a simple array
+  of addresses of the system calls, implement an arch_syscall_addr to return
+  the address of a given system call.
+- If the symbol names of the system calls do not match the function names on
+  this arch, define ARCH_HAS_SYSCALL_MATCH_SYM_NAME in asm/ftrace.h and
+  implement arch_syscall_match_sym_name with the appropriate logic to return
+  true if the function name corresponds with the symbol name.
+- Tag this arch as HAVE_SYSCALL_TRACEPOINTS.
+
+
+HAVE_FTRACE_MCOUNT_RECORD
+-------------------------
+
+See scripts/recordmcount.pl for more info.  Just fill in the arch-specific
+details for how to locate the addresses of mcount call sites via objdump.
+This option doesn't make much sense without also implementing dynamic ftrace.
+
+
+HAVE_DYNAMIC_FTRACE
+-------------------
+
+You will first need HAVE_FTRACE_MCOUNT_RECORD and HAVE_FUNCTION_TRACER, so
+scroll your reader back up if you got over eager.
+
+Once those are out of the way, you will need to implement:
+	- asm/ftrace.h:
+		- MCOUNT_ADDR
+		- ftrace_call_adjust()
+		- struct dyn_arch_ftrace{}
+	- asm code:
+		- mcount() (new stub)
+		- ftrace_caller()
+		- ftrace_call()
+		- ftrace_stub()
+	- C code:
+		- ftrace_dyn_arch_init()
+		- ftrace_make_nop()
+		- ftrace_make_call()
+		- ftrace_update_ftrace_func()
+
+First you will need to fill out some arch details in your asm/ftrace.h.
+
+Define MCOUNT_ADDR as the address of your mcount symbol similar to:
+	#define MCOUNT_ADDR ((unsigned long)mcount)
+Since no one else will have a decl for that function, you will need to:
+	extern void mcount(void);
+
+You will also need the helper function ftrace_call_adjust().  Most people
+will be able to stub it out like so:
+	static inline unsigned long ftrace_call_adjust(unsigned long addr)
+	{
+		return addr;
+	}
+<details to be filled>
+
+Lastly you will need the custom dyn_arch_ftrace structure.  If you need
+some extra state when runtime patching arbitrary call sites, this is the
+place.  For now though, create an empty struct:
+	struct dyn_arch_ftrace {
+		/* No extra data needed */
+	};
+
+With the header out of the way, we can fill out the assembly code.  While we
+did already create a mcount() function earlier, dynamic ftrace only wants a
+stub function.  This is because the mcount() will only be used during boot
+and then all references to it will be patched out never to return.  Instead,
+the guts of the old mcount() will be used to create a new ftrace_caller()
+function.  Because the two are hard to merge, it will most likely be a lot
+easier to have two separate definitions split up by #ifdefs.  Same goes for
+the ftrace_stub() as that will now be inlined in ftrace_caller().
+
+Before we get confused anymore, let's check out some pseudo code so you can
+implement your own stuff in assembly:
+
+void mcount(void)
+{
+	return;
+}
+
+void ftrace_caller(void)
+{
+	/* save all state needed by the ABI (see paragraph above) */
+
+	unsigned long frompc = ...;
+	unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE;
+
+ftrace_call:
+	ftrace_stub(frompc, selfpc);
+
+	/* restore all state needed by the ABI */
+
+ftrace_stub:
+	return;
+}
+
+This might look a little odd at first, but keep in mind that we will be runtime
+patching multiple things.  First, only functions that we actually want to trace
+will be patched to call ftrace_caller().  Second, since we only have one tracer
+active at a time, we will patch the ftrace_caller() function itself to call the
+specific tracer in question.  That is the point of the ftrace_call label.
+
+With that in mind, let's move on to the C code that will actually be doing the
+runtime patching.  You'll need a little knowledge of your arch's opcodes in
+order to make it through the next section.
+
+Every arch has an init callback function.  If you need to do something early on
+to initialize some state, this is the time to do that.  Otherwise, this simple
+function below should be sufficient for most people:
+
+int __init ftrace_dyn_arch_init(void)
+{
+	return 0;
+}
+
+There are two functions that are used to do runtime patching of arbitrary
+functions.  The first is used to turn the mcount call site into a nop (which
+is what helps us retain runtime performance when not tracing).  The second is
+used to turn the mcount call site into a call to an arbitrary location (but
+typically that is ftracer_caller()).  See the general function definition in
+linux/ftrace.h for the functions:
+	ftrace_make_nop()
+	ftrace_make_call()
+The rec->ip value is the address of the mcount call site that was collected
+by the scripts/recordmcount.pl during build time.
+
+The last function is used to do runtime patching of the active tracer.  This
+will be modifying the assembly code at the location of the ftrace_call symbol
+inside of the ftrace_caller() function.  So you should have sufficient padding
+at that location to support the new function calls you'll be inserting.  Some
+people will be using a "call" type instruction while others will be using a
+"branch" type instruction.  Specifically, the function is:
+	ftrace_update_ftrace_func()
+
+
+HAVE_DYNAMIC_FTRACE + HAVE_FUNCTION_GRAPH_TRACER
+------------------------------------------------
+
+The function grapher needs a few tweaks in order to work with dynamic ftrace.
+Basically, you will need to:
+	- update:
+		- ftrace_caller()
+		- ftrace_graph_call()
+		- ftrace_graph_caller()
+	- implement:
+		- ftrace_enable_ftrace_graph_caller()
+		- ftrace_disable_ftrace_graph_caller()
+
+<details to be filled>
+Quick notes:
+	- add a nop stub after the ftrace_call location named ftrace_graph_call;
+	  stub needs to be large enough to support a call to ftrace_graph_caller()
+	- update ftrace_graph_caller() to work with being called by the new
+	  ftrace_caller() since some semantics may have changed
+	- ftrace_enable_ftrace_graph_caller() will runtime patch the
+	  ftrace_graph_call location with a call to ftrace_graph_caller()
+	- ftrace_disable_ftrace_graph_caller() will runtime patch the
+	  ftrace_graph_call location with nops
diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
new file mode 100644
index 000000000..572ca9236
--- /dev/null
+++ b/Documentation/trace/ftrace.txt
@@ -0,0 +1,2846 @@
+		ftrace - Function Tracer
+		========================
+
+Copyright 2008 Red Hat Inc.
+   Author:   Steven Rostedt <srostedt@redhat.com>
+  License:   The GNU Free Documentation License, Version 1.2
+               (dual licensed under the GPL v2)
+Reviewers:   Elias Oltmanns, Randy Dunlap, Andrew Morton,
+	     John Kacur, and David Teigland.
+Written for: 2.6.28-rc2
+Updated for: 3.10
+
+Introduction
+------------
+
+Ftrace is an internal tracer designed to help out developers and
+designers of systems to find what is going on inside the kernel.
+It can be used for debugging or analyzing latencies and
+performance issues that take place outside of user-space.
+
+Although ftrace is typically considered the function tracer, it
+is really a frame work of several assorted tracing utilities.
+There's latency tracing to examine what occurs between interrupts
+disabled and enabled, as well as for preemption and from a time
+a task is woken to the task is actually scheduled in.
+
+One of the most common uses of ftrace is the event tracing.
+Through out the kernel is hundreds of static event points that
+can be enabled via the debugfs file system to see what is
+going on in certain parts of the kernel.
+
+
+Implementation Details
+----------------------
+
+See ftrace-design.txt for details for arch porters and such.
+
+
+The File System
+---------------
+
+Ftrace uses the debugfs file system to hold the control files as
+well as the files to display output.
+
+When debugfs is configured into the kernel (which selecting any ftrace
+option will do) the directory /sys/kernel/debug will be created. To mount
+this directory, you can add to your /etc/fstab file:
+
+ debugfs       /sys/kernel/debug          debugfs defaults        0       0
+
+Or you can mount it at run time with:
+
+ mount -t debugfs nodev /sys/kernel/debug
+
+For quicker access to that directory you may want to make a soft link to
+it:
+
+ ln -s /sys/kernel/debug /debug
+
+Any selected ftrace option will also create a directory called tracing
+within the debugfs. The rest of the document will assume that you are in
+the ftrace directory (cd /sys/kernel/debug/tracing) and will only concentrate
+on the files within that directory and not distract from the content with
+the extended "/sys/kernel/debug/tracing" path name.
+
+That's it! (assuming that you have ftrace configured into your kernel)
+
+After mounting debugfs, you can see a directory called
+"tracing".  This directory contains the control and output files
+of ftrace. Here is a list of some of the key files:
+
+
+ Note: all time values are in microseconds.
+
+  current_tracer:
+
+	This is used to set or display the current tracer
+	that is configured.
+
+  available_tracers:
+
+	This holds the different types of tracers that
+	have been compiled into the kernel. The
+	tracers listed here can be configured by
+	echoing their name into current_tracer.
+
+  tracing_on:
+
+	This sets or displays whether writing to the trace
+	ring buffer is enabled. Echo 0 into this file to disable
+	the tracer or 1 to enable it. Note, this only disables
+	writing to the ring buffer, the tracing overhead may
+	still be occurring.
+
+  trace:
+
+	This file holds the output of the trace in a human
+	readable format (described below).
+
+  trace_pipe:
+
+	The output is the same as the "trace" file but this
+	file is meant to be streamed with live tracing.
+	Reads from this file will block until new data is
+	retrieved.  Unlike the "trace" file, this file is a
+	consumer. This means reading from this file causes
+	sequential reads to display more current data. Once
+	data is read from this file, it is consumed, and
+	will not be read again with a sequential read. The
+	"trace" file is static, and if the tracer is not
+	adding more data,they will display the same
+	information every time they are read.
+
+  trace_options:
+
+	This file lets the user control the amount of data
+	that is displayed in one of the above output
+	files. Options also exist to modify how a tracer
+	or events work (stack traces, timestamps, etc).
+
+  options:
+
+	This is a directory that has a file for every available
+	trace option (also in trace_options). Options may also be set
+	or cleared by writing a "1" or "0" respectively into the
+	corresponding file with the option name.
+
+  tracing_max_latency:
+
+	Some of the tracers record the max latency.
+	For example, the time interrupts are disabled.
+	This time is saved in this file. The max trace
+	will also be stored, and displayed by "trace".
+	A new max trace will only be recorded if the
+	latency is greater than the value in this
+	file. (in microseconds)
+
+  tracing_thresh:
+
+	Some latency tracers will record a trace whenever the
+	latency is greater than the number in this file.
+	Only active when the file contains a number greater than 0.
+	(in microseconds)
+
+  buffer_size_kb:
+
+	This sets or displays the number of kilobytes each CPU
+	buffer holds. By default, the trace buffers are the same size
+	for each CPU. The displayed number is the size of the
+	CPU buffer and not total size of all buffers. The
+	trace buffers are allocated in pages (blocks of memory
+	that the kernel uses for allocation, usually 4 KB in size).
+	If the last page allocated has room for more bytes
+	than requested, the rest of the page will be used,
+	making the actual allocation bigger than requested.
+	( Note, the size may not be a multiple of the page size
+	  due to buffer management meta-data. )
+
+  buffer_total_size_kb:
+
+	This displays the total combined size of all the trace buffers.
+
+  free_buffer:
+
+	If a process is performing the tracing, and the ring buffer
+	should be shrunk "freed" when the process is finished, even
+	if it were to be killed by a signal, this file can be used
+	for that purpose. On close of this file, the ring buffer will
+	be resized to its minimum size. Having a process that is tracing
+	also open this file, when the process exits its file descriptor
+	for this file will be closed, and in doing so, the ring buffer
+	will be "freed".
+
+	It may also stop tracing if disable_on_free option is set.
+
+  tracing_cpumask:
+
+	This is a mask that lets the user only trace
+	on specified CPUs. The format is a hex string
+	representing the CPUs.
+
+  set_ftrace_filter:
+
+	When dynamic ftrace is configured in (see the
+	section below "dynamic ftrace"), the code is dynamically
+	modified (code text rewrite) to disable calling of the
+	function profiler (mcount). This lets tracing be configured
+	in with practically no overhead in performance.  This also
+	has a side effect of enabling or disabling specific functions
+	to be traced. Echoing names of functions into this file
+	will limit the trace to only those functions.
+
+	This interface also allows for commands to be used. See the
+	"Filter commands" section for more details.
+
+  set_ftrace_notrace:
+
+	This has an effect opposite to that of
+	set_ftrace_filter. Any function that is added here will not
+	be traced. If a function exists in both set_ftrace_filter
+	and set_ftrace_notrace,	the function will _not_ be traced.
+
+  set_ftrace_pid:
+
+	Have the function tracer only trace a single thread.
+
+  set_graph_function:
+
+	Set a "trigger" function where tracing should start
+	with the function graph tracer (See the section
+	"dynamic ftrace" for more details).
+
+  available_filter_functions:
+
+	This lists the functions that ftrace
+	has processed and can trace. These are the function
+	names that you can pass to "set_ftrace_filter" or
+	"set_ftrace_notrace". (See the section "dynamic ftrace"
+	below for more details.)
+
+  enabled_functions:
+
+	This file is more for debugging ftrace, but can also be useful
+	in seeing if any function has a callback attached to it.
+	Not only does the trace infrastructure use ftrace function
+	trace utility, but other subsystems might too. This file
+	displays all functions that have a callback attached to them
+	as well as the number of callbacks that have been attached.
+	Note, a callback may also call multiple functions which will
+	not be listed in this count.
+
+	If the callback registered to be traced by a function with
+	the "save regs" attribute (thus even more overhead), a 'R'
+	will be displayed on the same line as the function that
+	is returning registers.
+
+	If the callback registered to be traced by a function with
+	the "ip modify" attribute (thus the regs->ip can be changed),
+	an 'I' will be displayed on the same line as the function that
+	can be overridden.
+
+  function_profile_enabled:
+
+	When set it will enable all functions with either the function
+	tracer, or if enabled, the function graph tracer. It will
+	keep a histogram of the number of functions that were called
+	and if run with the function graph tracer, it will also keep
+	track of the time spent in those functions. The histogram
+	content can be displayed in the files:
+
+	trace_stats/function<cpu> ( function0, function1, etc).
+
+  trace_stats:
+
+	A directory that holds different tracing stats.
+
+  kprobe_events:
+ 
+	Enable dynamic trace points. See kprobetrace.txt.
+
+  kprobe_profile:
+
+	Dynamic trace points stats. See kprobetrace.txt.
+
+  max_graph_depth:
+
+	Used with the function graph tracer. This is the max depth
+	it will trace into a function. Setting this to a value of
+	one will show only the first kernel function that is called
+	from user space.
+
+  printk_formats:
+
+	This is for tools that read the raw format files. If an event in
+	the ring buffer references a string (currently only trace_printk()
+	does this), only a pointer to the string is recorded into the buffer
+	and not the string itself. This prevents tools from knowing what
+	that string was. This file displays the string and address for
+	the string allowing tools to map the pointers to what the
+	strings were.
+
+  saved_cmdlines:
+
+	Only the pid of the task is recorded in a trace event unless
+	the event specifically saves the task comm as well. Ftrace
+	makes a cache of pid mappings to comms to try to display
+	comms for events. If a pid for a comm is not listed, then
+	"<...>" is displayed in the output.
+
+  snapshot:
+
+	This displays the "snapshot" buffer and also lets the user
+	take a snapshot of the current running trace.
+	See the "Snapshot" section below for more details.
+
+  stack_max_size:
+
+	When the stack tracer is activated, this will display the
+	maximum stack size it has encountered.
+	See the "Stack Trace" section below.
+
+  stack_trace:
+
+	This displays the stack back trace of the largest stack
+	that was encountered when the stack tracer is activated.
+	See the "Stack Trace" section below.
+
+  stack_trace_filter:
+
+	This is similar to "set_ftrace_filter" but it limits what
+	functions the stack tracer will check.
+
+  trace_clock:
+
+	Whenever an event is recorded into the ring buffer, a
+	"timestamp" is added. This stamp comes from a specified
+	clock. By default, ftrace uses the "local" clock. This
+	clock is very fast and strictly per cpu, but on some
+	systems it may not be monotonic with respect to other
+	CPUs. In other words, the local clocks may not be in sync
+	with local clocks on other CPUs.
+
+	Usual clocks for tracing:
+
+	  # cat trace_clock
+	  [local] global counter x86-tsc
+
+	  local: Default clock, but may not be in sync across CPUs
+
+	  global: This clock is in sync with all CPUs but may
+	  	  be a bit slower than the local clock.
+
+	  counter: This is not a clock at all, but literally an atomic
+	  	   counter. It counts up one by one, but is in sync
+		   with all CPUs. This is useful when you need to
+		   know exactly the order events occurred with respect to
+		   each other on different CPUs.
+
+	  uptime: This uses the jiffies counter and the time stamp
+	  	  is relative to the time since boot up.
+
+	  perf: This makes ftrace use the same clock that perf uses.
+	  	Eventually perf will be able to read ftrace buffers
+		and this will help out in interleaving the data.
+
+	  x86-tsc: Architectures may define their own clocks. For
+	  	   example, x86 uses its own TSC cycle clock here.
+
+	To set a clock, simply echo the clock name into this file.
+
+	  echo global > trace_clock
+
+  trace_marker:
+
+	This is a very useful file for synchronizing user space
+	with events happening in the kernel. Writing strings into
+	this file will be written into the ftrace buffer.
+
+	It is useful in applications to open this file at the start
+	of the application and just reference the file descriptor
+	for the file.
+
+	void trace_write(const char *fmt, ...)
+	{
+		va_list ap;
+		char buf[256];
+		int n;
+
+		if (trace_fd < 0)
+			return;
+
+		va_start(ap, fmt);
+		n = vsnprintf(buf, 256, fmt, ap);
+		va_end(ap);
+
+		write(trace_fd, buf, n);
+	}
+
+	start:
+
+		trace_fd = open("trace_marker", WR_ONLY);
+
+  uprobe_events:
+ 
+	Add dynamic tracepoints in programs.
+	See uprobetracer.txt
+
+  uprobe_profile:
+
+	Uprobe statistics. See uprobetrace.txt
+
+  instances:
+
+	This is a way to make multiple trace buffers where different
+	events can be recorded in different buffers.
+	See "Instances" section below.
+
+  events:
+
+	This is the trace event directory. It holds event tracepoints
+	(also known as static tracepoints) that have been compiled
+	into the kernel. It shows what event tracepoints exist
+	and how they are grouped by system. There are "enable"
+	files at various levels that can enable the tracepoints
+	when a "1" is written to them.
+
+	See events.txt for more information.
+
+  per_cpu:
+
+	This is a directory that contains the trace per_cpu information.
+
+  per_cpu/cpu0/buffer_size_kb:
+
+	The ftrace buffer is defined per_cpu. That is, there's a separate
+	buffer for each CPU to allow writes to be done atomically,
+	and free from cache bouncing. These buffers may have different
+	size buffers. This file is similar to the buffer_size_kb
+	file, but it only displays or sets the buffer size for the
+	specific CPU. (here cpu0).
+
+  per_cpu/cpu0/trace:
+
+	This is similar to the "trace" file, but it will only display
+	the data specific for the CPU. If written to, it only clears
+	the specific CPU buffer.
+
+  per_cpu/cpu0/trace_pipe
+
+	This is similar to the "trace_pipe" file, and is a consuming
+	read, but it will only display (and consume) the data specific
+	for the CPU.
+
+  per_cpu/cpu0/trace_pipe_raw
+
+	For tools that can parse the ftrace ring buffer binary format,
+	the trace_pipe_raw file can be used to extract the data
+	from the ring buffer directly. With the use of the splice()
+	system call, the buffer data can be quickly transferred to
+	a file or to the network where a server is collecting the
+	data.
+
+	Like trace_pipe, this is a consuming reader, where multiple
+	reads will always produce different data.
+
+  per_cpu/cpu0/snapshot:
+
+	This is similar to the main "snapshot" file, but will only
+	snapshot the current CPU (if supported). It only displays
+	the content of the snapshot for a given CPU, and if
+	written to, only clears this CPU buffer.
+
+  per_cpu/cpu0/snapshot_raw:
+
+	Similar to the trace_pipe_raw, but will read the binary format
+	from the snapshot buffer for the given CPU.
+
+  per_cpu/cpu0/stats:
+
+	This displays certain stats about the ring buffer:
+
+	 entries: The number of events that are still in the buffer.
+
+	 overrun: The number of lost events due to overwriting when
+	 	  the buffer was full.
+
+	 commit overrun: Should always be zero.
+	 	This gets set if so many events happened within a nested
+		event (ring buffer is re-entrant), that it fills the
+		buffer and starts dropping events.
+
+	 bytes: Bytes actually read (not overwritten).
+
+	 oldest event ts: The oldest timestamp in the buffer
+
+	 now ts: The current timestamp
+
+	 dropped events: Events lost due to overwrite option being off.
+
+	 read events: The number of events read.
+
+The Tracers
+-----------
+
+Here is the list of current tracers that may be configured.
+
+  "function"
+
+	Function call tracer to trace all kernel functions.
+
+  "function_graph"
+
+	Similar to the function tracer except that the
+	function tracer probes the functions on their entry
+	whereas the function graph tracer traces on both entry
+	and exit of the functions. It then provides the ability
+	to draw a graph of function calls similar to C code
+	source.
+
+  "irqsoff"
+
+	Traces the areas that disable interrupts and saves
+	the trace with the longest max latency.
+	See tracing_max_latency. When a new max is recorded,
+	it replaces the old trace. It is best to view this
+	trace with the latency-format option enabled.
+
+  "preemptoff"
+
+	Similar to irqsoff but traces and records the amount of
+	time for which preemption is disabled.
+
+  "preemptirqsoff"
+
+	Similar to irqsoff and preemptoff, but traces and
+	records the largest time for which irqs and/or preemption
+	is disabled.
+
+  "wakeup"
+
+	Traces and records the max latency that it takes for
+	the highest priority task to get scheduled after
+	it has been woken up.
+        Traces all tasks as an average developer would expect.
+
+  "wakeup_rt"
+
+        Traces and records the max latency that it takes for just
+        RT tasks (as the current "wakeup" does). This is useful
+        for those interested in wake up timings of RT tasks.
+
+  "nop"
+
+	This is the "trace nothing" tracer. To remove all
+	tracers from tracing simply echo "nop" into
+	current_tracer.
+
+
+Examples of using the tracer
+----------------------------
+
+Here are typical examples of using the tracers when controlling
+them only with the debugfs interface (without using any
+user-land utilities).
+
+Output format:
+--------------
+
+Here is an example of the output format of the file "trace"
+
+                             --------
+# tracer: function
+#
+# entries-in-buffer/entries-written: 140080/250280   #P:4
+#
+#                              _-----=> irqs-off
+#                             / _----=> need-resched
+#                            | / _---=> hardirq/softirq
+#                            || / _--=> preempt-depth
+#                            ||| /     delay
+#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+#              | |       |   ||||       |         |
+            bash-1977  [000] .... 17284.993652: sys_close <-system_call_fastpath
+            bash-1977  [000] .... 17284.993653: __close_fd <-sys_close
+            bash-1977  [000] .... 17284.993653: _raw_spin_lock <-__close_fd
+            sshd-1974  [003] .... 17284.993653: __srcu_read_unlock <-fsnotify
+            bash-1977  [000] .... 17284.993654: add_preempt_count <-_raw_spin_lock
+            bash-1977  [000] ...1 17284.993655: _raw_spin_unlock <-__close_fd
+            bash-1977  [000] ...1 17284.993656: sub_preempt_count <-_raw_spin_unlock
+            bash-1977  [000] .... 17284.993657: filp_close <-__close_fd
+            bash-1977  [000] .... 17284.993657: dnotify_flush <-filp_close
+            sshd-1974  [003] .... 17284.993658: sys_select <-system_call_fastpath
+                             --------
+
+A header is printed with the tracer name that is represented by
+the trace. In this case the tracer is "function". Then it shows the
+number of events in the buffer as well as the total number of entries
+that were written. The difference is the number of entries that were
+lost due to the buffer filling up (250280 - 140080 = 110200 events
+lost).
+
+The header explains the content of the events. Task name "bash", the task
+PID "1977", the CPU that it was running on "000", the latency format
+(explained below), the timestamp in <secs>.<usecs> format, the
+function name that was traced "sys_close" and the parent function that
+called this function "system_call_fastpath". The timestamp is the time
+at which the function was entered.
+
+Latency trace format
+--------------------
+
+When the latency-format option is enabled or when one of the latency
+tracers is set, the trace file gives somewhat more information to see
+why a latency happened. Here is a typical trace.
+
+# tracer: irqsoff
+#
+# irqsoff latency trace v1.1.5 on 3.8.0-test+
+# --------------------------------------------------------------------
+# latency: 259 us, #4/4, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+#    -----------------
+#    | task: ps-6143 (uid:0 nice:0 policy:0 rt_prio:0)
+#    -----------------
+#  => started at: __lock_task_sighand
+#  => ended at:   _raw_spin_unlock_irqrestore
+#
+#
+#                  _------=> CPU#            
+#                 / _-----=> irqs-off        
+#                | / _----=> need-resched    
+#                || / _---=> hardirq/softirq 
+#                ||| / _--=> preempt-depth   
+#                |||| /     delay             
+#  cmd     pid   ||||| time  |   caller      
+#     \   /      |||||  \    |   /           
+      ps-6143    2d...    0us!: trace_hardirqs_off <-__lock_task_sighand
+      ps-6143    2d..1  259us+: trace_hardirqs_on <-_raw_spin_unlock_irqrestore
+      ps-6143    2d..1  263us+: time_hardirqs_on <-_raw_spin_unlock_irqrestore
+      ps-6143    2d..1  306us : <stack trace>
+ => trace_hardirqs_on_caller
+ => trace_hardirqs_on
+ => _raw_spin_unlock_irqrestore
+ => do_task_stat
+ => proc_tgid_stat
+ => proc_single_show
+ => seq_read
+ => vfs_read
+ => sys_read
+ => system_call_fastpath
+
+
+This shows that the current tracer is "irqsoff" tracing the time
+for which interrupts were disabled. It gives the trace version (which
+never changes) and the version of the kernel upon which this was executed on
+(3.10). Then it displays the max latency in microseconds (259 us). The number
+of trace entries displayed and the total number (both are four: #4/4).
+VP, KP, SP, and HP are always zero and are reserved for later use.
+#P is the number of online CPUs (#P:4).
+
+The task is the process that was running when the latency
+occurred. (ps pid: 6143).
+
+The start and stop (the functions in which the interrupts were
+disabled and enabled respectively) that caused the latencies:
+
+ __lock_task_sighand is where the interrupts were disabled.
+ _raw_spin_unlock_irqrestore is where they were enabled again.
+
+The next lines after the header are the trace itself. The header
+explains which is which.
+
+  cmd: The name of the process in the trace.
+
+  pid: The PID of that process.
+
+  CPU#: The CPU which the process was running on.
+
+  irqs-off: 'd' interrupts are disabled. '.' otherwise.
+	    Note: If the architecture does not support a way to
+		  read the irq flags variable, an 'X' will always
+		  be printed here.
+
+  need-resched:
+	'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set,
+	'n' only TIF_NEED_RESCHED is set,
+	'p' only PREEMPT_NEED_RESCHED is set,
+	'.' otherwise.
+
+  hardirq/softirq:
+	'H' - hard irq occurred inside a softirq.
+	'h' - hard irq is running
+	's' - soft irq is running
+	'.' - normal context.
+
+  preempt-depth: The level of preempt_disabled
+
+The above is mostly meaningful for kernel developers.
+
+  time: When the latency-format option is enabled, the trace file
+	output includes a timestamp relative to the start of the
+	trace. This differs from the output when latency-format
+	is disabled, which includes an absolute timestamp.
+
+  delay: This is just to help catch your eye a bit better. And
+	 needs to be fixed to be only relative to the same CPU.
+	 The marks are determined by the difference between this
+	 current trace and the next trace.
+	  '$' - greater than 1 second
+	  '#' - greater than 1000 microsecond
+	  '!' - greater than 100 microsecond
+	  '+' - greater than 10 microsecond
+	  ' ' - less than or equal to 10 microsecond.
+
+  The rest is the same as the 'trace' file.
+
+  Note, the latency tracers will usually end with a back trace
+  to easily find where the latency occurred.
+
+trace_options
+-------------
+
+The trace_options file (or the options directory) is used to control
+what gets printed in the trace output, or manipulate the tracers.
+To see what is available, simply cat the file:
+
+  cat trace_options
+print-parent
+nosym-offset
+nosym-addr
+noverbose
+noraw
+nohex
+nobin
+noblock
+nostacktrace
+trace_printk
+noftrace_preempt
+nobranch
+annotate
+nouserstacktrace
+nosym-userobj
+noprintk-msg-only
+context-info
+latency-format
+sleep-time
+graph-time
+record-cmd
+overwrite
+nodisable_on_free
+irq-info
+markers
+function-trace
+
+To disable one of the options, echo in the option prepended with
+"no".
+
+  echo noprint-parent > trace_options
+
+To enable an option, leave off the "no".
+
+  echo sym-offset > trace_options
+
+Here are the available options:
+
+  print-parent - On function traces, display the calling (parent)
+		 function as well as the function being traced.
+
+  print-parent:
+   bash-4000  [01]  1477.606694: simple_strtoul <-kstrtoul
+
+  noprint-parent:
+   bash-4000  [01]  1477.606694: simple_strtoul
+
+
+  sym-offset - Display not only the function name, but also the
+	       offset in the function. For example, instead of
+	       seeing just "ktime_get", you will see
+	       "ktime_get+0xb/0x20".
+
+  sym-offset:
+   bash-4000  [01]  1477.606694: simple_strtoul+0x6/0xa0
+
+  sym-addr - this will also display the function address as well
+	     as the function name.
+
+  sym-addr:
+   bash-4000  [01]  1477.606694: simple_strtoul <c0339346>
+
+  verbose - This deals with the trace file when the
+            latency-format option is enabled.
+
+    bash  4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \
+    (+0.000ms): simple_strtoul (kstrtoul)
+
+  raw - This will display raw numbers. This option is best for
+	use with user applications that can translate the raw
+	numbers better than having it done in the kernel.
+
+  hex - Similar to raw, but the numbers will be in a hexadecimal
+	format.
+
+  bin - This will print out the formats in raw binary.
+
+  block - When set, reading trace_pipe will not block when polled.
+
+  stacktrace - This is one of the options that changes the trace
+	       itself. When a trace is recorded, so is the stack
+	       of functions. This allows for back traces of
+	       trace sites.
+
+  trace_printk - Can disable trace_printk() from writing into the buffer.
+
+  branch - Enable branch tracing with the tracer.
+
+  annotate - It is sometimes confusing when the CPU buffers are full
+  	     and one CPU buffer had a lot of events recently, thus
+	     a shorter time frame, were another CPU may have only had
+	     a few events, which lets it have older events. When
+	     the trace is reported, it shows the oldest events first,
+	     and it may look like only one CPU ran (the one with the
+	     oldest events). When the annotate option is set, it will
+	     display when a new CPU buffer started:
+
+          <idle>-0     [001] dNs4 21169.031481: wake_up_idle_cpu <-add_timer_on
+          <idle>-0     [001] dNs4 21169.031482: _raw_spin_unlock_irqrestore <-add_timer_on
+          <idle>-0     [001] .Ns4 21169.031484: sub_preempt_count <-_raw_spin_unlock_irqrestore
+##### CPU 2 buffer started ####
+          <idle>-0     [002] .N.1 21169.031484: rcu_idle_exit <-cpu_idle
+          <idle>-0     [001] .Ns3 21169.031484: _raw_spin_unlock <-clocksource_watchdog
+          <idle>-0     [001] .Ns3 21169.031485: sub_preempt_count <-_raw_spin_unlock
+
+  userstacktrace - This option changes the trace. It records a
+		   stacktrace of the current userspace thread.
+
+  sym-userobj - when user stacktrace are enabled, look up which
+		object the address belongs to, and print a
+		relative address. This is especially useful when
+		ASLR is on, otherwise you don't get a chance to
+		resolve the address to object/file/line after
+		the app is no longer running
+
+		The lookup is performed when you read
+		trace,trace_pipe. Example:
+
+		a.out-1623  [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0
+x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
+
+
+  printk-msg-only - When set, trace_printk()s will only show the format
+  		    and not their parameters (if trace_bprintk() or
+		    trace_bputs() was used to save the trace_printk()).
+
+  context-info - Show only the event data. Hides the comm, PID,
+  	         timestamp, CPU, and other useful data.
+
+  latency-format - This option changes the trace. When
+                   it is enabled, the trace displays
+                   additional information about the
+                   latencies, as described in "Latency
+                   trace format".
+
+  sleep-time - When running function graph tracer, to include
+  	       the time a task schedules out in its function.
+	       When enabled, it will account time the task has been
+	       scheduled out as part of the function call.
+
+  graph-time - When running function graph tracer, to include the
+  	       time to call nested functions. When this is not set,
+	       the time reported for the function will only include
+	       the time the function itself executed for, not the time
+	       for functions that it called.
+
+  record-cmd - When any event or tracer is enabled, a hook is enabled
+  	       in the sched_switch trace point to fill comm cache
+	       with mapped pids and comms. But this may cause some
+	       overhead, and if you only care about pids, and not the
+	       name of the task, disabling this option can lower the
+	       impact of tracing.
+
+  overwrite - This controls what happens when the trace buffer is
+              full. If "1" (default), the oldest events are
+              discarded and overwritten. If "0", then the newest
+              events are discarded.
+	        (see per_cpu/cpu0/stats for overrun and dropped)
+
+  disable_on_free - When the free_buffer is closed, tracing will
+  		    stop (tracing_on set to 0).
+
+  irq-info - Shows the interrupt, preempt count, need resched data.
+  	     When disabled, the trace looks like:
+
+# tracer: function
+#
+# entries-in-buffer/entries-written: 144405/9452052   #P:4
+#
+#           TASK-PID   CPU#      TIMESTAMP  FUNCTION
+#              | |       |          |         |
+          <idle>-0     [002]  23636.756054: ttwu_do_activate.constprop.89 <-try_to_wake_up
+          <idle>-0     [002]  23636.756054: activate_task <-ttwu_do_activate.constprop.89
+          <idle>-0     [002]  23636.756055: enqueue_task <-activate_task
+
+
+  markers - When set, the trace_marker is writable (only by root).
+  	    When disabled, the trace_marker will error with EINVAL
+	    on write.
+
+
+  function-trace - The latency tracers will enable function tracing
+  	    if this option is enabled (default it is). When
+	    it is disabled, the latency tracers do not trace
+	    functions. This keeps the overhead of the tracer down
+	    when performing latency tests.
+
+ Note: Some tracers have their own options. They only appear
+       when the tracer is active.
+
+
+
+irqsoff
+-------
+
+When interrupts are disabled, the CPU can not react to any other
+external event (besides NMIs and SMIs). This prevents the timer
+interrupt from triggering or the mouse interrupt from letting
+the kernel know of a new mouse event. The result is a latency
+with the reaction time.
+
+The irqsoff tracer tracks the time for which interrupts are
+disabled. When a new maximum latency is hit, the tracer saves
+the trace leading up to that latency point so that every time a
+new maximum is reached, the old saved trace is discarded and the
+new trace is saved.
+
+To reset the maximum, echo 0 into tracing_max_latency. Here is
+an example:
+
+ # echo 0 > options/function-trace
+ # echo irqsoff > current_tracer
+ # echo 1 > tracing_on
+ # echo 0 > tracing_max_latency
+ # ls -ltr
+ [...]
+ # echo 0 > tracing_on
+ # cat trace
+# tracer: irqsoff
+#
+# irqsoff latency trace v1.1.5 on 3.8.0-test+
+# --------------------------------------------------------------------
+# latency: 16 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+#    -----------------
+#    | task: swapper/0-0 (uid:0 nice:0 policy:0 rt_prio:0)
+#    -----------------
+#  => started at: run_timer_softirq
+#  => ended at:   run_timer_softirq
+#
+#
+#                  _------=> CPU#            
+#                 / _-----=> irqs-off        
+#                | / _----=> need-resched    
+#                || / _---=> hardirq/softirq 
+#                ||| / _--=> preempt-depth   
+#                |||| /     delay             
+#  cmd     pid   ||||| time  |   caller      
+#     \   /      |||||  \    |   /           
+  <idle>-0       0d.s2    0us+: _raw_spin_lock_irq <-run_timer_softirq
+  <idle>-0       0dNs3   17us : _raw_spin_unlock_irq <-run_timer_softirq
+  <idle>-0       0dNs3   17us+: trace_hardirqs_on <-run_timer_softirq
+  <idle>-0       0dNs3   25us : <stack trace>
+ => _raw_spin_unlock_irq
+ => run_timer_softirq
+ => __do_softirq
+ => call_softirq
+ => do_softirq
+ => irq_exit
+ => smp_apic_timer_interrupt
+ => apic_timer_interrupt
+ => rcu_idle_exit
+ => cpu_idle
+ => rest_init
+ => start_kernel
+ => x86_64_start_reservations
+ => x86_64_start_kernel
+
+Here we see that that we had a latency of 16 microseconds (which is
+very good). The _raw_spin_lock_irq in run_timer_softirq disabled
+interrupts. The difference between the 16 and the displayed
+timestamp 25us occurred because the clock was incremented
+between the time of recording the max latency and the time of
+recording the function that had that latency.
+
+Note the above example had function-trace not set. If we set
+function-trace, we get a much larger output:
+
+ with echo 1 > options/function-trace
+
+# tracer: irqsoff
+#
+# irqsoff latency trace v1.1.5 on 3.8.0-test+
+# --------------------------------------------------------------------
+# latency: 71 us, #168/168, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+#    -----------------
+#    | task: bash-2042 (uid:0 nice:0 policy:0 rt_prio:0)
+#    -----------------
+#  => started at: ata_scsi_queuecmd
+#  => ended at:   ata_scsi_queuecmd
+#
+#
+#                  _------=> CPU#            
+#                 / _-----=> irqs-off        
+#                | / _----=> need-resched    
+#                || / _---=> hardirq/softirq 
+#                ||| / _--=> preempt-depth   
+#                |||| /     delay             
+#  cmd     pid   ||||| time  |   caller      
+#     \   /      |||||  \    |   /           
+    bash-2042    3d...    0us : _raw_spin_lock_irqsave <-ata_scsi_queuecmd
+    bash-2042    3d...    0us : add_preempt_count <-_raw_spin_lock_irqsave
+    bash-2042    3d..1    1us : ata_scsi_find_dev <-ata_scsi_queuecmd
+    bash-2042    3d..1    1us : __ata_scsi_find_dev <-ata_scsi_find_dev
+    bash-2042    3d..1    2us : ata_find_dev.part.14 <-__ata_scsi_find_dev
+    bash-2042    3d..1    2us : ata_qc_new_init <-__ata_scsi_queuecmd
+    bash-2042    3d..1    3us : ata_sg_init <-__ata_scsi_queuecmd
+    bash-2042    3d..1    4us : ata_scsi_rw_xlat <-__ata_scsi_queuecmd
+    bash-2042    3d..1    4us : ata_build_rw_tf <-ata_scsi_rw_xlat
+[...]
+    bash-2042    3d..1   67us : delay_tsc <-__delay
+    bash-2042    3d..1   67us : add_preempt_count <-delay_tsc
+    bash-2042    3d..2   67us : sub_preempt_count <-delay_tsc
+    bash-2042    3d..1   67us : add_preempt_count <-delay_tsc
+    bash-2042    3d..2   68us : sub_preempt_count <-delay_tsc
+    bash-2042    3d..1   68us+: ata_bmdma_start <-ata_bmdma_qc_issue
+    bash-2042    3d..1   71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
+    bash-2042    3d..1   71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
+    bash-2042    3d..1   72us+: trace_hardirqs_on <-ata_scsi_queuecmd
+    bash-2042    3d..1  120us : <stack trace>
+ => _raw_spin_unlock_irqrestore
+ => ata_scsi_queuecmd
+ => scsi_dispatch_cmd
+ => scsi_request_fn
+ => __blk_run_queue_uncond
+ => __blk_run_queue
+ => blk_queue_bio
+ => generic_make_request
+ => submit_bio
+ => submit_bh
+ => __ext3_get_inode_loc
+ => ext3_iget
+ => ext3_lookup
+ => lookup_real
+ => __lookup_hash
+ => walk_component
+ => lookup_last
+ => path_lookupat
+ => filename_lookup
+ => user_path_at_empty
+ => user_path_at
+ => vfs_fstatat
+ => vfs_stat
+ => sys_newstat
+ => system_call_fastpath
+
+
+Here we traced a 71 microsecond latency. But we also see all the
+functions that were called during that time. Note that by
+enabling function tracing, we incur an added overhead. This
+overhead may extend the latency times. But nevertheless, this
+trace has provided some very helpful debugging information.
+
+
+preemptoff
+----------
+
+When preemption is disabled, we may be able to receive
+interrupts but the task cannot be preempted and a higher
+priority task must wait for preemption to be enabled again
+before it can preempt a lower priority task.
+
+The preemptoff tracer traces the places that disable preemption.
+Like the irqsoff tracer, it records the maximum latency for
+which preemption was disabled. The control of preemptoff tracer
+is much like the irqsoff tracer.
+
+ # echo 0 > options/function-trace
+ # echo preemptoff > current_tracer
+ # echo 1 > tracing_on
+ # echo 0 > tracing_max_latency
+ # ls -ltr
+ [...]
+ # echo 0 > tracing_on
+ # cat trace
+# tracer: preemptoff
+#
+# preemptoff latency trace v1.1.5 on 3.8.0-test+
+# --------------------------------------------------------------------
+# latency: 46 us, #4/4, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+#    -----------------
+#    | task: sshd-1991 (uid:0 nice:0 policy:0 rt_prio:0)
+#    -----------------
+#  => started at: do_IRQ
+#  => ended at:   do_IRQ
+#
+#
+#                  _------=> CPU#            
+#                 / _-----=> irqs-off        
+#                | / _----=> need-resched    
+#                || / _---=> hardirq/softirq 
+#                ||| / _--=> preempt-depth   
+#                |||| /     delay             
+#  cmd     pid   ||||| time  |   caller      
+#     \   /      |||||  \    |   /           
+    sshd-1991    1d.h.    0us+: irq_enter <-do_IRQ
+    sshd-1991    1d..1   46us : irq_exit <-do_IRQ
+    sshd-1991    1d..1   47us+: trace_preempt_on <-do_IRQ
+    sshd-1991    1d..1   52us : <stack trace>
+ => sub_preempt_count
+ => irq_exit
+ => do_IRQ
+ => ret_from_intr
+
+
+This has some more changes. Preemption was disabled when an
+interrupt came in (notice the 'h'), and was enabled on exit.
+But we also see that interrupts have been disabled when entering
+the preempt off section and leaving it (the 'd'). We do not know if
+interrupts were enabled in the mean time or shortly after this
+was over.
+
+# tracer: preemptoff
+#
+# preemptoff latency trace v1.1.5 on 3.8.0-test+
+# --------------------------------------------------------------------
+# latency: 83 us, #241/241, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+#    -----------------
+#    | task: bash-1994 (uid:0 nice:0 policy:0 rt_prio:0)
+#    -----------------
+#  => started at: wake_up_new_task
+#  => ended at:   task_rq_unlock
+#
+#
+#                  _------=> CPU#            
+#                 / _-----=> irqs-off        
+#                | / _----=> need-resched    
+#                || / _---=> hardirq/softirq 
+#                ||| / _--=> preempt-depth   
+#                |||| /     delay             
+#  cmd     pid   ||||| time  |   caller      
+#     \   /      |||||  \    |   /           
+    bash-1994    1d..1    0us : _raw_spin_lock_irqsave <-wake_up_new_task
+    bash-1994    1d..1    0us : select_task_rq_fair <-select_task_rq
+    bash-1994    1d..1    1us : __rcu_read_lock <-select_task_rq_fair
+    bash-1994    1d..1    1us : source_load <-select_task_rq_fair
+    bash-1994    1d..1    1us : source_load <-select_task_rq_fair
+[...]
+    bash-1994    1d..1   12us : irq_enter <-smp_apic_timer_interrupt
+    bash-1994    1d..1   12us : rcu_irq_enter <-irq_enter
+    bash-1994    1d..1   13us : add_preempt_count <-irq_enter
+    bash-1994    1d.h1   13us : exit_idle <-smp_apic_timer_interrupt
+    bash-1994    1d.h1   13us : hrtimer_interrupt <-smp_apic_timer_interrupt
+    bash-1994    1d.h1   13us : _raw_spin_lock <-hrtimer_interrupt
+    bash-1994    1d.h1   14us : add_preempt_count <-_raw_spin_lock
+    bash-1994    1d.h2   14us : ktime_get_update_offsets <-hrtimer_interrupt
+[...]
+    bash-1994    1d.h1   35us : lapic_next_event <-clockevents_program_event
+    bash-1994    1d.h1   35us : irq_exit <-smp_apic_timer_interrupt
+    bash-1994    1d.h1   36us : sub_preempt_count <-irq_exit
+    bash-1994    1d..2   36us : do_softirq <-irq_exit
+    bash-1994    1d..2   36us : __do_softirq <-call_softirq
+    bash-1994    1d..2   36us : __local_bh_disable <-__do_softirq
+    bash-1994    1d.s2   37us : add_preempt_count <-_raw_spin_lock_irq
+    bash-1994    1d.s3   38us : _raw_spin_unlock <-run_timer_softirq
+    bash-1994    1d.s3   39us : sub_preempt_count <-_raw_spin_unlock
+    bash-1994    1d.s2   39us : call_timer_fn <-run_timer_softirq
+[...]
+    bash-1994    1dNs2   81us : cpu_needs_another_gp <-rcu_process_callbacks
+    bash-1994    1dNs2   82us : __local_bh_enable <-__do_softirq
+    bash-1994    1dNs2   82us : sub_preempt_count <-__local_bh_enable
+    bash-1994    1dN.2   82us : idle_cpu <-irq_exit
+    bash-1994    1dN.2   83us : rcu_irq_exit <-irq_exit
+    bash-1994    1dN.2   83us : sub_preempt_count <-irq_exit
+    bash-1994    1.N.1   84us : _raw_spin_unlock_irqrestore <-task_rq_unlock
+    bash-1994    1.N.1   84us+: trace_preempt_on <-task_rq_unlock
+    bash-1994    1.N.1  104us : <stack trace>
+ => sub_preempt_count
+ => _raw_spin_unlock_irqrestore
+ => task_rq_unlock
+ => wake_up_new_task
+ => do_fork
+ => sys_clone
+ => stub_clone
+
+
+The above is an example of the preemptoff trace with
+function-trace set. Here we see that interrupts were not disabled
+the entire time. The irq_enter code lets us know that we entered
+an interrupt 'h'. Before that, the functions being traced still
+show that it is not in an interrupt, but we can see from the
+functions themselves that this is not the case.
+
+preemptirqsoff
+--------------
+
+Knowing the locations that have interrupts disabled or
+preemption disabled for the longest times is helpful. But
+sometimes we would like to know when either preemption and/or
+interrupts are disabled.
+
+Consider the following code:
+
+    local_irq_disable();
+    call_function_with_irqs_off();
+    preempt_disable();
+    call_function_with_irqs_and_preemption_off();
+    local_irq_enable();
+    call_function_with_preemption_off();
+    preempt_enable();
+
+The irqsoff tracer will record the total length of
+call_function_with_irqs_off() and
+call_function_with_irqs_and_preemption_off().
+
+The preemptoff tracer will record the total length of
+call_function_with_irqs_and_preemption_off() and
+call_function_with_preemption_off().
+
+But neither will trace the time that interrupts and/or
+preemption is disabled. This total time is the time that we can
+not schedule. To record this time, use the preemptirqsoff
+tracer.
+
+Again, using this trace is much like the irqsoff and preemptoff
+tracers.
+
+ # echo 0 > options/function-trace
+ # echo preemptirqsoff > current_tracer
+ # echo 1 > tracing_on
+ # echo 0 > tracing_max_latency
+ # ls -ltr
+ [...]
+ # echo 0 > tracing_on
+ # cat trace
+# tracer: preemptirqsoff
+#
+# preemptirqsoff latency trace v1.1.5 on 3.8.0-test+
+# --------------------------------------------------------------------
+# latency: 100 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+#    -----------------
+#    | task: ls-2230 (uid:0 nice:0 policy:0 rt_prio:0)
+#    -----------------
+#  => started at: ata_scsi_queuecmd
+#  => ended at:   ata_scsi_queuecmd
+#
+#
+#                  _------=> CPU#            
+#                 / _-----=> irqs-off        
+#                | / _----=> need-resched    
+#                || / _---=> hardirq/softirq 
+#                ||| / _--=> preempt-depth   
+#                |||| /     delay             
+#  cmd     pid   ||||| time  |   caller      
+#     \   /      |||||  \    |   /           
+      ls-2230    3d...    0us+: _raw_spin_lock_irqsave <-ata_scsi_queuecmd
+      ls-2230    3...1  100us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
+      ls-2230    3...1  101us+: trace_preempt_on <-ata_scsi_queuecmd
+      ls-2230    3...1  111us : <stack trace>
+ => sub_preempt_count
+ => _raw_spin_unlock_irqrestore
+ => ata_scsi_queuecmd
+ => scsi_dispatch_cmd
+ => scsi_request_fn
+ => __blk_run_queue_uncond
+ => __blk_run_queue
+ => blk_queue_bio
+ => generic_make_request
+ => submit_bio
+ => submit_bh
+ => ext3_bread
+ => ext3_dir_bread
+ => htree_dirblock_to_tree
+ => ext3_htree_fill_tree
+ => ext3_readdir
+ => vfs_readdir
+ => sys_getdents
+ => system_call_fastpath
+
+
+The trace_hardirqs_off_thunk is called from assembly on x86 when
+interrupts are disabled in the assembly code. Without the
+function tracing, we do not know if interrupts were enabled
+within the preemption points. We do see that it started with
+preemption enabled.
+
+Here is a trace with function-trace set:
+
+# tracer: preemptirqsoff
+#
+# preemptirqsoff latency trace v1.1.5 on 3.8.0-test+
+# --------------------------------------------------------------------
+# latency: 161 us, #339/339, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+#    -----------------
+#    | task: ls-2269 (uid:0 nice:0 policy:0 rt_prio:0)
+#    -----------------
+#  => started at: schedule
+#  => ended at:   mutex_unlock
+#
+#
+#                  _------=> CPU#            
+#                 / _-----=> irqs-off        
+#                | / _----=> need-resched    
+#                || / _---=> hardirq/softirq 
+#                ||| / _--=> preempt-depth   
+#                |||| /     delay             
+#  cmd     pid   ||||| time  |   caller      
+#     \   /      |||||  \    |   /           
+kworker/-59      3...1    0us : __schedule <-schedule
+kworker/-59      3d..1    0us : rcu_preempt_qs <-rcu_note_context_switch
+kworker/-59      3d..1    1us : add_preempt_count <-_raw_spin_lock_irq
+kworker/-59      3d..2    1us : deactivate_task <-__schedule
+kworker/-59      3d..2    1us : dequeue_task <-deactivate_task
+kworker/-59      3d..2    2us : update_rq_clock <-dequeue_task
+kworker/-59      3d..2    2us : dequeue_task_fair <-dequeue_task
+kworker/-59      3d..2    2us : update_curr <-dequeue_task_fair
+kworker/-59      3d..2    2us : update_min_vruntime <-update_curr
+kworker/-59      3d..2    3us : cpuacct_charge <-update_curr
+kworker/-59      3d..2    3us : __rcu_read_lock <-cpuacct_charge
+kworker/-59      3d..2    3us : __rcu_read_unlock <-cpuacct_charge
+kworker/-59      3d..2    3us : update_cfs_rq_blocked_load <-dequeue_task_fair
+kworker/-59      3d..2    4us : clear_buddies <-dequeue_task_fair
+kworker/-59      3d..2    4us : account_entity_dequeue <-dequeue_task_fair
+kworker/-59      3d..2    4us : update_min_vruntime <-dequeue_task_fair
+kworker/-59      3d..2    4us : update_cfs_shares <-dequeue_task_fair
+kworker/-59      3d..2    5us : hrtick_update <-dequeue_task_fair
+kworker/-59      3d..2    5us : wq_worker_sleeping <-__schedule
+kworker/-59      3d..2    5us : kthread_data <-wq_worker_sleeping
+kworker/-59      3d..2    5us : put_prev_task_fair <-__schedule
+kworker/-59      3d..2    6us : pick_next_task_fair <-pick_next_task
+kworker/-59      3d..2    6us : clear_buddies <-pick_next_task_fair
+kworker/-59      3d..2    6us : set_next_entity <-pick_next_task_fair
+kworker/-59      3d..2    6us : update_stats_wait_end <-set_next_entity
+      ls-2269    3d..2    7us : finish_task_switch <-__schedule
+      ls-2269    3d..2    7us : _raw_spin_unlock_irq <-finish_task_switch
+      ls-2269    3d..2    8us : do_IRQ <-ret_from_intr
+      ls-2269    3d..2    8us : irq_enter <-do_IRQ
+      ls-2269    3d..2    8us : rcu_irq_enter <-irq_enter
+      ls-2269    3d..2    9us : add_preempt_count <-irq_enter
+      ls-2269    3d.h2    9us : exit_idle <-do_IRQ
+[...]
+      ls-2269    3d.h3   20us : sub_preempt_count <-_raw_spin_unlock
+      ls-2269    3d.h2   20us : irq_exit <-do_IRQ
+      ls-2269    3d.h2   21us : sub_preempt_count <-irq_exit
+      ls-2269    3d..3   21us : do_softirq <-irq_exit
+      ls-2269    3d..3   21us : __do_softirq <-call_softirq
+      ls-2269    3d..3   21us+: __local_bh_disable <-__do_softirq
+      ls-2269    3d.s4   29us : sub_preempt_count <-_local_bh_enable_ip
+      ls-2269    3d.s5   29us : sub_preempt_count <-_local_bh_enable_ip
+      ls-2269    3d.s5   31us : do_IRQ <-ret_from_intr
+      ls-2269    3d.s5   31us : irq_enter <-do_IRQ
+      ls-2269    3d.s5   31us : rcu_irq_enter <-irq_enter
+[...]
+      ls-2269    3d.s5   31us : rcu_irq_enter <-irq_enter
+      ls-2269    3d.s5   32us : add_preempt_count <-irq_enter
+      ls-2269    3d.H5   32us : exit_idle <-do_IRQ
+      ls-2269    3d.H5   32us : handle_irq <-do_IRQ
+      ls-2269    3d.H5   32us : irq_to_desc <-handle_irq
+      ls-2269    3d.H5   33us : handle_fasteoi_irq <-handle_irq
+[...]
+      ls-2269    3d.s5  158us : _raw_spin_unlock_irqrestore <-rtl8139_poll
+      ls-2269    3d.s3  158us : net_rps_action_and_irq_enable.isra.65 <-net_rx_action
+      ls-2269    3d.s3  159us : __local_bh_enable <-__do_softirq
+      ls-2269    3d.s3  159us : sub_preempt_count <-__local_bh_enable
+      ls-2269    3d..3  159us : idle_cpu <-irq_exit
+      ls-2269    3d..3  159us : rcu_irq_exit <-irq_exit
+      ls-2269    3d..3  160us : sub_preempt_count <-irq_exit
+      ls-2269    3d...  161us : __mutex_unlock_slowpath <-mutex_unlock
+      ls-2269    3d...  162us+: trace_hardirqs_on <-mutex_unlock
+      ls-2269    3d...  186us : <stack trace>
+ => __mutex_unlock_slowpath
+ => mutex_unlock
+ => process_output
+ => n_tty_write
+ => tty_write
+ => vfs_write
+ => sys_write
+ => system_call_fastpath
+
+This is an interesting trace. It started with kworker running and
+scheduling out and ls taking over. But as soon as ls released the
+rq lock and enabled interrupts (but not preemption) an interrupt
+triggered. When the interrupt finished, it started running softirqs.
+But while the softirq was running, another interrupt triggered.
+When an interrupt is running inside a softirq, the annotation is 'H'.
+
+
+wakeup
+------
+
+One common case that people are interested in tracing is the
+time it takes for a task that is woken to actually wake up.
+Now for non Real-Time tasks, this can be arbitrary. But tracing
+it none the less can be interesting. 
+
+Without function tracing:
+
+ # echo 0 > options/function-trace
+ # echo wakeup > current_tracer
+ # echo 1 > tracing_on
+ # echo 0 > tracing_max_latency
+ # chrt -f 5 sleep 1
+ # echo 0 > tracing_on
+ # cat trace
+# tracer: wakeup
+#
+# wakeup latency trace v1.1.5 on 3.8.0-test+
+# --------------------------------------------------------------------
+# latency: 15 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+#    -----------------
+#    | task: kworker/3:1H-312 (uid:0 nice:-20 policy:0 rt_prio:0)
+#    -----------------
+#
+#                  _------=> CPU#            
+#                 / _-----=> irqs-off        
+#                | / _----=> need-resched    
+#                || / _---=> hardirq/softirq 
+#                ||| / _--=> preempt-depth   
+#                |||| /     delay             
+#  cmd     pid   ||||| time  |   caller      
+#     \   /      |||||  \    |   /           
+  <idle>-0       3dNs7    0us :      0:120:R   + [003]   312:100:R kworker/3:1H
+  <idle>-0       3dNs7    1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up
+  <idle>-0       3d..3   15us : __schedule <-schedule
+  <idle>-0       3d..3   15us :      0:120:R ==> [003]   312:100:R kworker/3:1H
+
+The tracer only traces the highest priority task in the system
+to avoid tracing the normal circumstances. Here we see that
+the kworker with a nice priority of -20 (not very nice), took
+just 15 microseconds from the time it woke up, to the time it
+ran.
+
+Non Real-Time tasks are not that interesting. A more interesting
+trace is to concentrate only on Real-Time tasks.
+
+wakeup_rt
+---------
+
+In a Real-Time environment it is very important to know the
+wakeup time it takes for the highest priority task that is woken
+up to the time that it executes. This is also known as "schedule
+latency". I stress the point that this is about RT tasks. It is
+also important to know the scheduling latency of non-RT tasks,
+but the average schedule latency is better for non-RT tasks.
+Tools like LatencyTop are more appropriate for such
+measurements.
+
+Real-Time environments are interested in the worst case latency.
+That is the longest latency it takes for something to happen,
+and not the average. We can have a very fast scheduler that may
+only have a large latency once in a while, but that would not
+work well with Real-Time tasks.  The wakeup_rt tracer was designed
+to record the worst case wakeups of RT tasks. Non-RT tasks are
+not recorded because the tracer only records one worst case and
+tracing non-RT tasks that are unpredictable will overwrite the
+worst case latency of RT tasks (just run the normal wakeup
+tracer for a while to see that effect).
+
+Since this tracer only deals with RT tasks, we will run this
+slightly differently than we did with the previous tracers.
+Instead of performing an 'ls', we will run 'sleep 1' under
+'chrt' which changes the priority of the task.
+
+ # echo 0 > options/function-trace
+ # echo wakeup_rt > current_tracer
+ # echo 1 > tracing_on
+ # echo 0 > tracing_max_latency
+ # chrt -f 5 sleep 1
+ # echo 0 > tracing_on
+ # cat trace
+# tracer: wakeup
+#
+# tracer: wakeup_rt
+#
+# wakeup_rt latency trace v1.1.5 on 3.8.0-test+
+# --------------------------------------------------------------------
+# latency: 5 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+#    -----------------
+#    | task: sleep-2389 (uid:0 nice:0 policy:1 rt_prio:5)
+#    -----------------
+#
+#                  _------=> CPU#            
+#                 / _-----=> irqs-off        
+#                | / _----=> need-resched    
+#                || / _---=> hardirq/softirq 
+#                ||| / _--=> preempt-depth   
+#                |||| /     delay             
+#  cmd     pid   ||||| time  |   caller      
+#     \   /      |||||  \    |   /           
+  <idle>-0       3d.h4    0us :      0:120:R   + [003]  2389: 94:R sleep
+  <idle>-0       3d.h4    1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up
+  <idle>-0       3d..3    5us : __schedule <-schedule
+  <idle>-0       3d..3    5us :      0:120:R ==> [003]  2389: 94:R sleep
+
+
+Running this on an idle system, we see that it only took 5 microseconds
+to perform the task switch.  Note, since the trace point in the schedule
+is before the actual "switch", we stop the tracing when the recorded task
+is about to schedule in. This may change if we add a new marker at the
+end of the scheduler.
+
+Notice that the recorded task is 'sleep' with the PID of 2389
+and it has an rt_prio of 5. This priority is user-space priority
+and not the internal kernel priority. The policy is 1 for
+SCHED_FIFO and 2 for SCHED_RR.
+
+Note, that the trace data shows the internal priority (99 - rtprio).
+
+  <idle>-0       3d..3    5us :      0:120:R ==> [003]  2389: 94:R sleep
+
+The 0:120:R means idle was running with a nice priority of 0 (120 - 20)
+and in the running state 'R'. The sleep task was scheduled in with
+2389: 94:R. That is the priority is the kernel rtprio (99 - 5 = 94)
+and it too is in the running state.
+
+Doing the same with chrt -r 5 and function-trace set.
+
+  echo 1 > options/function-trace
+
+# tracer: wakeup_rt
+#
+# wakeup_rt latency trace v1.1.5 on 3.8.0-test+
+# --------------------------------------------------------------------
+# latency: 29 us, #85/85, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+#    -----------------
+#    | task: sleep-2448 (uid:0 nice:0 policy:1 rt_prio:5)
+#    -----------------
+#
+#                  _------=> CPU#            
+#                 / _-----=> irqs-off        
+#                | / _----=> need-resched    
+#                || / _---=> hardirq/softirq 
+#                ||| / _--=> preempt-depth   
+#                |||| /     delay             
+#  cmd     pid   ||||| time  |   caller      
+#     \   /      |||||  \    |   /           
+  <idle>-0       3d.h4    1us+:      0:120:R   + [003]  2448: 94:R sleep
+  <idle>-0       3d.h4    2us : ttwu_do_activate.constprop.87 <-try_to_wake_up
+  <idle>-0       3d.h3    3us : check_preempt_curr <-ttwu_do_wakeup
+  <idle>-0       3d.h3    3us : resched_curr <-check_preempt_curr
+  <idle>-0       3dNh3    4us : task_woken_rt <-ttwu_do_wakeup
+  <idle>-0       3dNh3    4us : _raw_spin_unlock <-try_to_wake_up
+  <idle>-0       3dNh3    4us : sub_preempt_count <-_raw_spin_unlock
+  <idle>-0       3dNh2    5us : ttwu_stat <-try_to_wake_up
+  <idle>-0       3dNh2    5us : _raw_spin_unlock_irqrestore <-try_to_wake_up
+  <idle>-0       3dNh2    6us : sub_preempt_count <-_raw_spin_unlock_irqrestore
+  <idle>-0       3dNh1    6us : _raw_spin_lock <-__run_hrtimer
+  <idle>-0       3dNh1    6us : add_preempt_count <-_raw_spin_lock
+  <idle>-0       3dNh2    7us : _raw_spin_unlock <-hrtimer_interrupt
+  <idle>-0       3dNh2    7us : sub_preempt_count <-_raw_spin_unlock
+  <idle>-0       3dNh1    7us : tick_program_event <-hrtimer_interrupt
+  <idle>-0       3dNh1    7us : clockevents_program_event <-tick_program_event
+  <idle>-0       3dNh1    8us : ktime_get <-clockevents_program_event
+  <idle>-0       3dNh1    8us : lapic_next_event <-clockevents_program_event
+  <idle>-0       3dNh1    8us : irq_exit <-smp_apic_timer_interrupt
+  <idle>-0       3dNh1    9us : sub_preempt_count <-irq_exit
+  <idle>-0       3dN.2    9us : idle_cpu <-irq_exit
+  <idle>-0       3dN.2    9us : rcu_irq_exit <-irq_exit
+  <idle>-0       3dN.2   10us : rcu_eqs_enter_common.isra.45 <-rcu_irq_exit
+  <idle>-0       3dN.2   10us : sub_preempt_count <-irq_exit
+  <idle>-0       3.N.1   11us : rcu_idle_exit <-cpu_idle
+  <idle>-0       3dN.1   11us : rcu_eqs_exit_common.isra.43 <-rcu_idle_exit
+  <idle>-0       3.N.1   11us : tick_nohz_idle_exit <-cpu_idle
+  <idle>-0       3dN.1   12us : menu_hrtimer_cancel <-tick_nohz_idle_exit
+  <idle>-0       3dN.1   12us : ktime_get <-tick_nohz_idle_exit
+  <idle>-0       3dN.1   12us : tick_do_update_jiffies64 <-tick_nohz_idle_exit
+  <idle>-0       3dN.1   13us : update_cpu_load_nohz <-tick_nohz_idle_exit
+  <idle>-0       3dN.1   13us : _raw_spin_lock <-update_cpu_load_nohz
+  <idle>-0       3dN.1   13us : add_preempt_count <-_raw_spin_lock
+  <idle>-0       3dN.2   13us : __update_cpu_load <-update_cpu_load_nohz
+  <idle>-0       3dN.2   14us : sched_avg_update <-__update_cpu_load
+  <idle>-0       3dN.2   14us : _raw_spin_unlock <-update_cpu_load_nohz
+  <idle>-0       3dN.2   14us : sub_preempt_count <-_raw_spin_unlock
+  <idle>-0       3dN.1   15us : calc_load_exit_idle <-tick_nohz_idle_exit
+  <idle>-0       3dN.1   15us : touch_softlockup_watchdog <-tick_nohz_idle_exit
+  <idle>-0       3dN.1   15us : hrtimer_cancel <-tick_nohz_idle_exit
+  <idle>-0       3dN.1   15us : hrtimer_try_to_cancel <-hrtimer_cancel
+  <idle>-0       3dN.1   16us : lock_hrtimer_base.isra.18 <-hrtimer_try_to_cancel
+  <idle>-0       3dN.1   16us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18
+  <idle>-0       3dN.1   16us : add_preempt_count <-_raw_spin_lock_irqsave
+  <idle>-0       3dN.2   17us : __remove_hrtimer <-remove_hrtimer.part.16
+  <idle>-0       3dN.2   17us : hrtimer_force_reprogram <-__remove_hrtimer
+  <idle>-0       3dN.2   17us : tick_program_event <-hrtimer_force_reprogram
+  <idle>-0       3dN.2   18us : clockevents_program_event <-tick_program_event
+  <idle>-0       3dN.2   18us : ktime_get <-clockevents_program_event
+  <idle>-0       3dN.2   18us : lapic_next_event <-clockevents_program_event
+  <idle>-0       3dN.2   19us : _raw_spin_unlock_irqrestore <-hrtimer_try_to_cancel
+  <idle>-0       3dN.2   19us : sub_preempt_count <-_raw_spin_unlock_irqrestore
+  <idle>-0       3dN.1   19us : hrtimer_forward <-tick_nohz_idle_exit
+  <idle>-0       3dN.1   20us : ktime_add_safe <-hrtimer_forward
+  <idle>-0       3dN.1   20us : ktime_add_safe <-hrtimer_forward
+  <idle>-0       3dN.1   20us : hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11
+  <idle>-0       3dN.1   20us : __hrtimer_start_range_ns <-hrtimer_start_range_ns
+  <idle>-0       3dN.1   21us : lock_hrtimer_base.isra.18 <-__hrtimer_start_range_ns
+  <idle>-0       3dN.1   21us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18
+  <idle>-0       3dN.1   21us : add_preempt_count <-_raw_spin_lock_irqsave
+  <idle>-0       3dN.2   22us : ktime_add_safe <-__hrtimer_start_range_ns
+  <idle>-0       3dN.2   22us : enqueue_hrtimer <-__hrtimer_start_range_ns
+  <idle>-0       3dN.2   22us : tick_program_event <-__hrtimer_start_range_ns
+  <idle>-0       3dN.2   23us : clockevents_program_event <-tick_program_event
+  <idle>-0       3dN.2   23us : ktime_get <-clockevents_program_event
+  <idle>-0       3dN.2   23us : lapic_next_event <-clockevents_program_event
+  <idle>-0       3dN.2   24us : _raw_spin_unlock_irqrestore <-__hrtimer_start_range_ns
+  <idle>-0       3dN.2   24us : sub_preempt_count <-_raw_spin_unlock_irqrestore
+  <idle>-0       3dN.1   24us : account_idle_ticks <-tick_nohz_idle_exit
+  <idle>-0       3dN.1   24us : account_idle_time <-account_idle_ticks
+  <idle>-0       3.N.1   25us : sub_preempt_count <-cpu_idle
+  <idle>-0       3.N..   25us : schedule <-cpu_idle
+  <idle>-0       3.N..   25us : __schedule <-preempt_schedule
+  <idle>-0       3.N..   26us : add_preempt_count <-__schedule
+  <idle>-0       3.N.1   26us : rcu_note_context_switch <-__schedule
+  <idle>-0       3.N.1   26us : rcu_sched_qs <-rcu_note_context_switch
+  <idle>-0       3dN.1   27us : rcu_preempt_qs <-rcu_note_context_switch
+  <idle>-0       3.N.1   27us : _raw_spin_lock_irq <-__schedule
+  <idle>-0       3dN.1   27us : add_preempt_count <-_raw_spin_lock_irq
+  <idle>-0       3dN.2   28us : put_prev_task_idle <-__schedule
+  <idle>-0       3dN.2   28us : pick_next_task_stop <-pick_next_task
+  <idle>-0       3dN.2   28us : pick_next_task_rt <-pick_next_task
+  <idle>-0       3dN.2   29us : dequeue_pushable_task <-pick_next_task_rt
+  <idle>-0       3d..3   29us : __schedule <-preempt_schedule
+  <idle>-0       3d..3   30us :      0:120:R ==> [003]  2448: 94:R sleep
+
+This isn't that big of a trace, even with function tracing enabled,
+so I included the entire trace.
+
+The interrupt went off while when the system was idle. Somewhere
+before task_woken_rt() was called, the NEED_RESCHED flag was set,
+this is indicated by the first occurrence of the 'N' flag.
+
+Latency tracing and events
+--------------------------
+As function tracing can induce a much larger latency, but without
+seeing what happens within the latency it is hard to know what
+caused it. There is a middle ground, and that is with enabling
+events.
+
+ # echo 0 > options/function-trace
+ # echo wakeup_rt > current_tracer
+ # echo 1 > events/enable
+ # echo 1 > tracing_on
+ # echo 0 > tracing_max_latency
+ # chrt -f 5 sleep 1
+ # echo 0 > tracing_on
+ # cat trace
+# tracer: wakeup_rt
+#
+# wakeup_rt latency trace v1.1.5 on 3.8.0-test+
+# --------------------------------------------------------------------
+# latency: 6 us, #12/12, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+#    -----------------
+#    | task: sleep-5882 (uid:0 nice:0 policy:1 rt_prio:5)
+#    -----------------
+#
+#                  _------=> CPU#            
+#                 / _-----=> irqs-off        
+#                | / _----=> need-resched    
+#                || / _---=> hardirq/softirq 
+#                ||| / _--=> preempt-depth   
+#                |||| /     delay             
+#  cmd     pid   ||||| time  |   caller      
+#     \   /      |||||  \    |   /           
+  <idle>-0       2d.h4    0us :      0:120:R   + [002]  5882: 94:R sleep
+  <idle>-0       2d.h4    0us : ttwu_do_activate.constprop.87 <-try_to_wake_up
+  <idle>-0       2d.h4    1us : sched_wakeup: comm=sleep pid=5882 prio=94 success=1 target_cpu=002
+  <idle>-0       2dNh2    1us : hrtimer_expire_exit: hrtimer=ffff88007796feb8
+  <idle>-0       2.N.2    2us : power_end: cpu_id=2
+  <idle>-0       2.N.2    3us : cpu_idle: state=4294967295 cpu_id=2
+  <idle>-0       2dN.3    4us : hrtimer_cancel: hrtimer=ffff88007d50d5e0
+  <idle>-0       2dN.3    4us : hrtimer_start: hrtimer=ffff88007d50d5e0 function=tick_sched_timer expires=34311211000000 softexpires=34311211000000
+  <idle>-0       2.N.2    5us : rcu_utilization: Start context switch
+  <idle>-0       2.N.2    5us : rcu_utilization: End context switch
+  <idle>-0       2d..3    6us : __schedule <-schedule
+  <idle>-0       2d..3    6us :      0:120:R ==> [002]  5882: 94:R sleep
+
+
+function
+--------
+
+This tracer is the function tracer. Enabling the function tracer
+can be done from the debug file system. Make sure the
+ftrace_enabled is set; otherwise this tracer is a nop.
+See the "ftrace_enabled" section below.
+
+ # sysctl kernel.ftrace_enabled=1
+ # echo function > current_tracer
+ # echo 1 > tracing_on
+ # usleep 1
+ # echo 0 > tracing_on
+ # cat trace
+# tracer: function
+#
+# entries-in-buffer/entries-written: 24799/24799   #P:4
+#
+#                              _-----=> irqs-off
+#                             / _----=> need-resched
+#                            | / _---=> hardirq/softirq
+#                            || / _--=> preempt-depth
+#                            ||| /     delay
+#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+#              | |       |   ||||       |         |
+            bash-1994  [002] ....  3082.063030: mutex_unlock <-rb_simple_write
+            bash-1994  [002] ....  3082.063031: __mutex_unlock_slowpath <-mutex_unlock
+            bash-1994  [002] ....  3082.063031: __fsnotify_parent <-fsnotify_modify
+            bash-1994  [002] ....  3082.063032: fsnotify <-fsnotify_modify
+            bash-1994  [002] ....  3082.063032: __srcu_read_lock <-fsnotify
+            bash-1994  [002] ....  3082.063032: add_preempt_count <-__srcu_read_lock
+            bash-1994  [002] ...1  3082.063032: sub_preempt_count <-__srcu_read_lock
+            bash-1994  [002] ....  3082.063033: __srcu_read_unlock <-fsnotify
+[...]
+
+
+Note: function tracer uses ring buffers to store the above
+entries. The newest data may overwrite the oldest data.
+Sometimes using echo to stop the trace is not sufficient because
+the tracing could have overwritten the data that you wanted to
+record. For this reason, it is sometimes better to disable
+tracing directly from a program. This allows you to stop the
+tracing at the point that you hit the part that you are
+interested in. To disable the tracing directly from a C program,
+something like following code snippet can be used:
+
+int trace_fd;
+[...]
+int main(int argc, char *argv[]) {
+	[...]
+	trace_fd = open(tracing_file("tracing_on"), O_WRONLY);
+	[...]
+	if (condition_hit()) {
+		write(trace_fd, "0", 1);
+	}
+	[...]
+}
+
+
+Single thread tracing
+---------------------
+
+By writing into set_ftrace_pid you can trace a
+single thread. For example:
+
+# cat set_ftrace_pid
+no pid
+# echo 3111 > set_ftrace_pid
+# cat set_ftrace_pid
+3111
+# echo function > current_tracer
+# cat trace | head
+ # tracer: function
+ #
+ #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
+ #              | |       |          |         |
+     yum-updatesd-3111  [003]  1637.254676: finish_task_switch <-thread_return
+     yum-updatesd-3111  [003]  1637.254681: hrtimer_cancel <-schedule_hrtimeout_range
+     yum-updatesd-3111  [003]  1637.254682: hrtimer_try_to_cancel <-hrtimer_cancel
+     yum-updatesd-3111  [003]  1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel
+     yum-updatesd-3111  [003]  1637.254685: fget_light <-do_sys_poll
+     yum-updatesd-3111  [003]  1637.254686: pipe_poll <-do_sys_poll
+# echo > set_ftrace_pid
+# cat trace |head
+ # tracer: function
+ #
+ #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
+ #              | |       |          |         |
+ ##### CPU 3 buffer started ####
+     yum-updatesd-3111  [003]  1701.957688: free_poll_entry <-poll_freewait
+     yum-updatesd-3111  [003]  1701.957689: remove_wait_queue <-free_poll_entry
+     yum-updatesd-3111  [003]  1701.957691: fput <-free_poll_entry
+     yum-updatesd-3111  [003]  1701.957692: audit_syscall_exit <-sysret_audit
+     yum-updatesd-3111  [003]  1701.957693: path_put <-audit_syscall_exit
+
+If you want to trace a function when executing, you could use
+something like this simple program:
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+
+#define _STR(x) #x
+#define STR(x) _STR(x)
+#define MAX_PATH 256
+
+const char *find_debugfs(void)
+{
+       static char debugfs[MAX_PATH+1];
+       static int debugfs_found;
+       char type[100];
+       FILE *fp;
+
+       if (debugfs_found)
+               return debugfs;
+
+       if ((fp = fopen("/proc/mounts","r")) == NULL) {
+               perror("/proc/mounts");
+               return NULL;
+       }
+
+       while (fscanf(fp, "%*s %"
+                     STR(MAX_PATH)
+                     "s %99s %*s %*d %*d\n",
+                     debugfs, type) == 2) {
+               if (strcmp(type, "debugfs") == 0)
+                       break;
+       }
+       fclose(fp);
+
+       if (strcmp(type, "debugfs") != 0) {
+               fprintf(stderr, "debugfs not mounted");
+               return NULL;
+       }
+
+       strcat(debugfs, "/tracing/");
+       debugfs_found = 1;
+
+       return debugfs;
+}
+
+const char *tracing_file(const char *file_name)
+{
+       static char trace_file[MAX_PATH+1];
+       snprintf(trace_file, MAX_PATH, "%s/%s", find_debugfs(), file_name);
+       return trace_file;
+}
+
+int main (int argc, char **argv)
+{
+        if (argc < 1)
+                exit(-1);
+
+        if (fork() > 0) {
+                int fd, ffd;
+                char line[64];
+                int s;
+
+                ffd = open(tracing_file("current_tracer"), O_WRONLY);
+                if (ffd < 0)
+                        exit(-1);
+                write(ffd, "nop", 3);
+
+                fd = open(tracing_file("set_ftrace_pid"), O_WRONLY);
+                s = sprintf(line, "%d\n", getpid());
+                write(fd, line, s);
+
+                write(ffd, "function", 8);
+
+                close(fd);
+                close(ffd);
+
+                execvp(argv[1], argv+1);
+        }
+
+        return 0;
+}
+
+Or this simple script!
+
+------
+#!/bin/bash
+
+debugfs=`sed -ne 's/^debugfs \(.*\) debugfs.*/\1/p' /proc/mounts`
+echo nop > $debugfs/tracing/current_tracer
+echo 0 > $debugfs/tracing/tracing_on
+echo $$ > $debugfs/tracing/set_ftrace_pid
+echo function > $debugfs/tracing/current_tracer
+echo 1 > $debugfs/tracing/tracing_on
+exec "$@"
+------
+
+
+function graph tracer
+---------------------------
+
+This tracer is similar to the function tracer except that it
+probes a function on its entry and its exit. This is done by
+using a dynamically allocated stack of return addresses in each
+task_struct. On function entry the tracer overwrites the return
+address of each function traced to set a custom probe. Thus the
+original return address is stored on the stack of return address
+in the task_struct.
+
+Probing on both ends of a function leads to special features
+such as:
+
+- measure of a function's time execution
+- having a reliable call stack to draw function calls graph
+
+This tracer is useful in several situations:
+
+- you want to find the reason of a strange kernel behavior and
+  need to see what happens in detail on any areas (or specific
+  ones).
+
+- you are experiencing weird latencies but it's difficult to
+  find its origin.
+
+- you want to find quickly which path is taken by a specific
+  function
+
+- you just want to peek inside a working kernel and want to see
+  what happens there.
+
+# tracer: function_graph
+#
+# CPU  DURATION                  FUNCTION CALLS
+# |     |   |                     |   |   |   |
+
+ 0)               |  sys_open() {
+ 0)               |    do_sys_open() {
+ 0)               |      getname() {
+ 0)               |        kmem_cache_alloc() {
+ 0)   1.382 us    |          __might_sleep();
+ 0)   2.478 us    |        }
+ 0)               |        strncpy_from_user() {
+ 0)               |          might_fault() {
+ 0)   1.389 us    |            __might_sleep();
+ 0)   2.553 us    |          }
+ 0)   3.807 us    |        }
+ 0)   7.876 us    |      }
+ 0)               |      alloc_fd() {
+ 0)   0.668 us    |        _spin_lock();
+ 0)   0.570 us    |        expand_files();
+ 0)   0.586 us    |        _spin_unlock();
+
+
+There are several columns that can be dynamically
+enabled/disabled. You can use every combination of options you
+want, depending on your needs.
+
+- The cpu number on which the function executed is default
+  enabled.  It is sometimes better to only trace one cpu (see
+  tracing_cpu_mask file) or you might sometimes see unordered
+  function calls while cpu tracing switch.
+
+	hide: echo nofuncgraph-cpu > trace_options
+	show: echo funcgraph-cpu > trace_options
+
+- The duration (function's time of execution) is displayed on
+  the closing bracket line of a function or on the same line
+  than the current function in case of a leaf one. It is default
+  enabled.
+
+	hide: echo nofuncgraph-duration > trace_options
+	show: echo funcgraph-duration > trace_options
+
+- The overhead field precedes the duration field in case of
+  reached duration thresholds.
+
+	hide: echo nofuncgraph-overhead > trace_options
+	show: echo funcgraph-overhead > trace_options
+	depends on: funcgraph-duration
+
+  ie:
+
+  0)               |    up_write() {
+  0)   0.646 us    |      _spin_lock_irqsave();
+  0)   0.684 us    |      _spin_unlock_irqrestore();
+  0)   3.123 us    |    }
+  0)   0.548 us    |    fput();
+  0) + 58.628 us   |  }
+
+  [...]
+
+  0)               |      putname() {
+  0)               |        kmem_cache_free() {
+  0)   0.518 us    |          __phys_addr();
+  0)   1.757 us    |        }
+  0)   2.861 us    |      }
+  0) ! 115.305 us  |    }
+  0) ! 116.402 us  |  }
+
+  + means that the function exceeded 10 usecs.
+  ! means that the function exceeded 100 usecs.
+  # means that the function exceeded 1000 usecs.
+  $ means that the function exceeded 1 sec.
+
+
+- The task/pid field displays the thread cmdline and pid which
+  executed the function. It is default disabled.
+
+	hide: echo nofuncgraph-proc > trace_options
+	show: echo funcgraph-proc > trace_options
+
+  ie:
+
+  # tracer: function_graph
+  #
+  # CPU  TASK/PID        DURATION                  FUNCTION CALLS
+  # |    |    |           |   |                     |   |   |   |
+  0)    sh-4802     |               |                  d_free() {
+  0)    sh-4802     |               |                    call_rcu() {
+  0)    sh-4802     |               |                      __call_rcu() {
+  0)    sh-4802     |   0.616 us    |                        rcu_process_gp_end();
+  0)    sh-4802     |   0.586 us    |                        check_for_new_grace_period();
+  0)    sh-4802     |   2.899 us    |                      }
+  0)    sh-4802     |   4.040 us    |                    }
+  0)    sh-4802     |   5.151 us    |                  }
+  0)    sh-4802     | + 49.370 us   |                }
+
+
+- The absolute time field is an absolute timestamp given by the
+  system clock since it started. A snapshot of this time is
+  given on each entry/exit of functions
+
+	hide: echo nofuncgraph-abstime > trace_options
+	show: echo funcgraph-abstime > trace_options
+
+  ie:
+
+  #
+  #      TIME       CPU  DURATION                  FUNCTION CALLS
+  #       |         |     |   |                     |   |   |   |
+  360.774522 |   1)   0.541 us    |                                          }
+  360.774522 |   1)   4.663 us    |                                        }
+  360.774523 |   1)   0.541 us    |                                        __wake_up_bit();
+  360.774524 |   1)   6.796 us    |                                      }
+  360.774524 |   1)   7.952 us    |                                    }
+  360.774525 |   1)   9.063 us    |                                  }
+  360.774525 |   1)   0.615 us    |                                  journal_mark_dirty();
+  360.774527 |   1)   0.578 us    |                                  __brelse();
+  360.774528 |   1)               |                                  reiserfs_prepare_for_journal() {
+  360.774528 |   1)               |                                    unlock_buffer() {
+  360.774529 |   1)               |                                      wake_up_bit() {
+  360.774529 |   1)               |                                        bit_waitqueue() {
+  360.774530 |   1)   0.594 us    |                                          __phys_addr();
+
+
+The function name is always displayed after the closing bracket
+for a function if the start of that function is not in the
+trace buffer.
+
+Display of the function name after the closing bracket may be
+enabled for functions whose start is in the trace buffer,
+allowing easier searching with grep for function durations.
+It is default disabled.
+
+	hide: echo nofuncgraph-tail > trace_options
+	show: echo funcgraph-tail > trace_options
+
+  Example with nofuncgraph-tail (default):
+  0)               |      putname() {
+  0)               |        kmem_cache_free() {
+  0)   0.518 us    |          __phys_addr();
+  0)   1.757 us    |        }
+  0)   2.861 us    |      }
+
+  Example with funcgraph-tail:
+  0)               |      putname() {
+  0)               |        kmem_cache_free() {
+  0)   0.518 us    |          __phys_addr();
+  0)   1.757 us    |        } /* kmem_cache_free() */
+  0)   2.861 us    |      } /* putname() */
+
+You can put some comments on specific functions by using
+trace_printk() For example, if you want to put a comment inside
+the __might_sleep() function, you just have to include
+<linux/ftrace.h> and call trace_printk() inside __might_sleep()
+
+trace_printk("I'm a comment!\n")
+
+will produce:
+
+ 1)               |             __might_sleep() {
+ 1)               |                /* I'm a comment! */
+ 1)   1.449 us    |             }
+
+
+You might find other useful features for this tracer in the
+following "dynamic ftrace" section such as tracing only specific
+functions or tasks.
+
+dynamic ftrace
+--------------
+
+If CONFIG_DYNAMIC_FTRACE is set, the system will run with
+virtually no overhead when function tracing is disabled. The way
+this works is the mcount function call (placed at the start of
+every kernel function, produced by the -pg switch in gcc),
+starts of pointing to a simple return. (Enabling FTRACE will
+include the -pg switch in the compiling of the kernel.)
+
+At compile time every C file object is run through the
+recordmcount program (located in the scripts directory). This
+program will parse the ELF headers in the C object to find all
+the locations in the .text section that call mcount. (Note, only
+white listed .text sections are processed, since processing other
+sections like .init.text may cause races due to those sections
+being freed unexpectedly).
+
+A new section called "__mcount_loc" is created that holds
+references to all the mcount call sites in the .text section.
+The recordmcount program re-links this section back into the
+original object. The final linking stage of the kernel will add all these
+references into a single table.
+
+On boot up, before SMP is initialized, the dynamic ftrace code
+scans this table and updates all the locations into nops. It
+also records the locations, which are added to the
+available_filter_functions list.  Modules are processed as they
+are loaded and before they are executed.  When a module is
+unloaded, it also removes its functions from the ftrace function
+list. This is automatic in the module unload code, and the
+module author does not need to worry about it.
+
+When tracing is enabled, the process of modifying the function
+tracepoints is dependent on architecture. The old method is to use
+kstop_machine to prevent races with the CPUs executing code being
+modified (which can cause the CPU to do undesirable things, especially
+if the modified code crosses cache (or page) boundaries), and the nops are
+patched back to calls. But this time, they do not call mcount
+(which is just a function stub). They now call into the ftrace
+infrastructure.
+
+The new method of modifying the function tracepoints is to place
+a breakpoint at the location to be modified, sync all CPUs, modify
+the rest of the instruction not covered by the breakpoint. Sync
+all CPUs again, and then remove the breakpoint with the finished
+version to the ftrace call site.
+
+Some archs do not even need to monkey around with the synchronization,
+and can just slap the new code on top of the old without any
+problems with other CPUs executing it at the same time.
+
+One special side-effect to the recording of the functions being
+traced is that we can now selectively choose which functions we
+wish to trace and which ones we want the mcount calls to remain
+as nops.
+
+Two files are used, one for enabling and one for disabling the
+tracing of specified functions. They are:
+
+  set_ftrace_filter
+
+and
+
+  set_ftrace_notrace
+
+A list of available functions that you can add to these files is
+listed in:
+
+   available_filter_functions
+
+ # cat available_filter_functions
+put_prev_task_idle
+kmem_cache_create
+pick_next_task_rt
+get_online_cpus
+pick_next_task_fair
+mutex_lock
+[...]
+
+If I am only interested in sys_nanosleep and hrtimer_interrupt:
+
+ # echo sys_nanosleep hrtimer_interrupt > set_ftrace_filter
+ # echo function > current_tracer
+ # echo 1 > tracing_on
+ # usleep 1
+ # echo 0 > tracing_on
+ # cat trace
+# tracer: function
+#
+# entries-in-buffer/entries-written: 5/5   #P:4
+#
+#                              _-----=> irqs-off
+#                             / _----=> need-resched
+#                            | / _---=> hardirq/softirq
+#                            || / _--=> preempt-depth
+#                            ||| /     delay
+#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+#              | |       |   ||||       |         |
+          usleep-2665  [001] ....  4186.475355: sys_nanosleep <-system_call_fastpath
+          <idle>-0     [001] d.h1  4186.475409: hrtimer_interrupt <-smp_apic_timer_interrupt
+          usleep-2665  [001] d.h1  4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt
+          <idle>-0     [003] d.h1  4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt
+          <idle>-0     [002] d.h1  4186.475427: hrtimer_interrupt <-smp_apic_timer_interrupt
+
+To see which functions are being traced, you can cat the file:
+
+ # cat set_ftrace_filter
+hrtimer_interrupt
+sys_nanosleep
+
+
+Perhaps this is not enough. The filters also allow simple wild
+cards. Only the following are currently available
+
+  <match>*  - will match functions that begin with <match>
+  *<match>  - will match functions that end with <match>
+  *<match>* - will match functions that have <match> in it
+
+These are the only wild cards which are supported.
+
+  <match>*<match> will not work.
+
+Note: It is better to use quotes to enclose the wild cards,
+      otherwise the shell may expand the parameters into names
+      of files in the local directory.
+
+ # echo 'hrtimer_*' > set_ftrace_filter
+
+Produces:
+
+# tracer: function
+#
+# entries-in-buffer/entries-written: 897/897   #P:4
+#
+#                              _-----=> irqs-off
+#                             / _----=> need-resched
+#                            | / _---=> hardirq/softirq
+#                            || / _--=> preempt-depth
+#                            ||| /     delay
+#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+#              | |       |   ||||       |         |
+          <idle>-0     [003] dN.1  4228.547803: hrtimer_cancel <-tick_nohz_idle_exit
+          <idle>-0     [003] dN.1  4228.547804: hrtimer_try_to_cancel <-hrtimer_cancel
+          <idle>-0     [003] dN.2  4228.547805: hrtimer_force_reprogram <-__remove_hrtimer
+          <idle>-0     [003] dN.1  4228.547805: hrtimer_forward <-tick_nohz_idle_exit
+          <idle>-0     [003] dN.1  4228.547805: hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11
+          <idle>-0     [003] d..1  4228.547858: hrtimer_get_next_event <-get_next_timer_interrupt
+          <idle>-0     [003] d..1  4228.547859: hrtimer_start <-__tick_nohz_idle_enter
+          <idle>-0     [003] d..2  4228.547860: hrtimer_force_reprogram <-__rem
+
+Notice that we lost the sys_nanosleep.
+
+ # cat set_ftrace_filter
+hrtimer_run_queues
+hrtimer_run_pending
+hrtimer_init
+hrtimer_cancel
+hrtimer_try_to_cancel
+hrtimer_forward
+hrtimer_start
+hrtimer_reprogram
+hrtimer_force_reprogram
+hrtimer_get_next_event
+hrtimer_interrupt
+hrtimer_nanosleep
+hrtimer_wakeup
+hrtimer_get_remaining
+hrtimer_get_res
+hrtimer_init_sleeper
+
+
+This is because the '>' and '>>' act just like they do in bash.
+To rewrite the filters, use '>'
+To append to the filters, use '>>'
+
+To clear out a filter so that all functions will be recorded
+again:
+
+ # echo > set_ftrace_filter
+ # cat set_ftrace_filter
+ #
+
+Again, now we want to append.
+
+ # echo sys_nanosleep > set_ftrace_filter
+ # cat set_ftrace_filter
+sys_nanosleep
+ # echo 'hrtimer_*' >> set_ftrace_filter
+ # cat set_ftrace_filter
+hrtimer_run_queues
+hrtimer_run_pending
+hrtimer_init
+hrtimer_cancel
+hrtimer_try_to_cancel
+hrtimer_forward
+hrtimer_start
+hrtimer_reprogram
+hrtimer_force_reprogram
+hrtimer_get_next_event
+hrtimer_interrupt
+sys_nanosleep
+hrtimer_nanosleep
+hrtimer_wakeup
+hrtimer_get_remaining
+hrtimer_get_res
+hrtimer_init_sleeper
+
+
+The set_ftrace_notrace prevents those functions from being
+traced.
+
+ # echo '*preempt*' '*lock*' > set_ftrace_notrace
+
+Produces:
+
+# tracer: function
+#
+# entries-in-buffer/entries-written: 39608/39608   #P:4
+#
+#                              _-----=> irqs-off
+#                             / _----=> need-resched
+#                            | / _---=> hardirq/softirq
+#                            || / _--=> preempt-depth
+#                            ||| /     delay
+#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+#              | |       |   ||||       |         |
+            bash-1994  [000] ....  4342.324896: file_ra_state_init <-do_dentry_open
+            bash-1994  [000] ....  4342.324897: open_check_o_direct <-do_last
+            bash-1994  [000] ....  4342.324897: ima_file_check <-do_last
+            bash-1994  [000] ....  4342.324898: process_measurement <-ima_file_check
+            bash-1994  [000] ....  4342.324898: ima_get_action <-process_measurement
+            bash-1994  [000] ....  4342.324898: ima_match_policy <-ima_get_action
+            bash-1994  [000] ....  4342.324899: do_truncate <-do_last
+            bash-1994  [000] ....  4342.324899: should_remove_suid <-do_truncate
+            bash-1994  [000] ....  4342.324899: notify_change <-do_truncate
+            bash-1994  [000] ....  4342.324900: current_fs_time <-notify_change
+            bash-1994  [000] ....  4342.324900: current_kernel_time <-current_fs_time
+            bash-1994  [000] ....  4342.324900: timespec_trunc <-current_fs_time
+
+We can see that there's no more lock or preempt tracing.
+
+
+Dynamic ftrace with the function graph tracer
+---------------------------------------------
+
+Although what has been explained above concerns both the
+function tracer and the function-graph-tracer, there are some
+special features only available in the function-graph tracer.
+
+If you want to trace only one function and all of its children,
+you just have to echo its name into set_graph_function:
+
+ echo __do_fault > set_graph_function
+
+will produce the following "expanded" trace of the __do_fault()
+function:
+
+ 0)               |  __do_fault() {
+ 0)               |    filemap_fault() {
+ 0)               |      find_lock_page() {
+ 0)   0.804 us    |        find_get_page();
+ 0)               |        __might_sleep() {
+ 0)   1.329 us    |        }
+ 0)   3.904 us    |      }
+ 0)   4.979 us    |    }
+ 0)   0.653 us    |    _spin_lock();
+ 0)   0.578 us    |    page_add_file_rmap();
+ 0)   0.525 us    |    native_set_pte_at();
+ 0)   0.585 us    |    _spin_unlock();
+ 0)               |    unlock_page() {
+ 0)   0.541 us    |      page_waitqueue();
+ 0)   0.639 us    |      __wake_up_bit();
+ 0)   2.786 us    |    }
+ 0) + 14.237 us   |  }
+ 0)               |  __do_fault() {
+ 0)               |    filemap_fault() {
+ 0)               |      find_lock_page() {
+ 0)   0.698 us    |        find_get_page();
+ 0)               |        __might_sleep() {
+ 0)   1.412 us    |        }
+ 0)   3.950 us    |      }
+ 0)   5.098 us    |    }
+ 0)   0.631 us    |    _spin_lock();
+ 0)   0.571 us    |    page_add_file_rmap();
+ 0)   0.526 us    |    native_set_pte_at();
+ 0)   0.586 us    |    _spin_unlock();
+ 0)               |    unlock_page() {
+ 0)   0.533 us    |      page_waitqueue();
+ 0)   0.638 us    |      __wake_up_bit();
+ 0)   2.793 us    |    }
+ 0) + 14.012 us   |  }
+
+You can also expand several functions at once:
+
+ echo sys_open > set_graph_function
+ echo sys_close >> set_graph_function
+
+Now if you want to go back to trace all functions you can clear
+this special filter via:
+
+ echo > set_graph_function
+
+
+ftrace_enabled
+--------------
+
+Note, the proc sysctl ftrace_enable is a big on/off switch for the
+function tracer. By default it is enabled (when function tracing is
+enabled in the kernel). If it is disabled, all function tracing is
+disabled. This includes not only the function tracers for ftrace, but
+also for any other uses (perf, kprobes, stack tracing, profiling, etc).
+
+Please disable this with care.
+
+This can be disable (and enabled) with:
+
+  sysctl kernel.ftrace_enabled=0
+  sysctl kernel.ftrace_enabled=1
+
+ or
+
+  echo 0 > /proc/sys/kernel/ftrace_enabled
+  echo 1 > /proc/sys/kernel/ftrace_enabled
+
+
+Filter commands
+---------------
+
+A few commands are supported by the set_ftrace_filter interface.
+Trace commands have the following format:
+
+<function>:<command>:<parameter>
+
+The following commands are supported:
+
+- mod
+  This command enables function filtering per module. The
+  parameter defines the module. For example, if only the write*
+  functions in the ext3 module are desired, run:
+
+   echo 'write*:mod:ext3' > set_ftrace_filter
+
+  This command interacts with the filter in the same way as
+  filtering based on function names. Thus, adding more functions
+  in a different module is accomplished by appending (>>) to the
+  filter file. Remove specific module functions by prepending
+  '!':
+
+   echo '!writeback*:mod:ext3' >> set_ftrace_filter
+
+- traceon/traceoff
+  These commands turn tracing on and off when the specified
+  functions are hit. The parameter determines how many times the
+  tracing system is turned on and off. If unspecified, there is
+  no limit. For example, to disable tracing when a schedule bug
+  is hit the first 5 times, run:
+
+   echo '__schedule_bug:traceoff:5' > set_ftrace_filter
+
+  To always disable tracing when __schedule_bug is hit:
+
+   echo '__schedule_bug:traceoff' > set_ftrace_filter
+
+  These commands are cumulative whether or not they are appended
+  to set_ftrace_filter. To remove a command, prepend it by '!'
+  and drop the parameter:
+
+   echo '!__schedule_bug:traceoff:0' > set_ftrace_filter
+
+    The above removes the traceoff command for __schedule_bug
+    that have a counter. To remove commands without counters:
+
+   echo '!__schedule_bug:traceoff' > set_ftrace_filter
+
+- snapshot
+  Will cause a snapshot to be triggered when the function is hit.
+
+   echo 'native_flush_tlb_others:snapshot' > set_ftrace_filter
+
+  To only snapshot once:
+
+   echo 'native_flush_tlb_others:snapshot:1' > set_ftrace_filter
+
+  To remove the above commands:
+
+   echo '!native_flush_tlb_others:snapshot' > set_ftrace_filter
+   echo '!native_flush_tlb_others:snapshot:0' > set_ftrace_filter
+
+- enable_event/disable_event
+  These commands can enable or disable a trace event. Note, because
+  function tracing callbacks are very sensitive, when these commands
+  are registered, the trace point is activated, but disabled in
+  a "soft" mode. That is, the tracepoint will be called, but
+  just will not be traced. The event tracepoint stays in this mode
+  as long as there's a command that triggers it.
+
+   echo 'try_to_wake_up:enable_event:sched:sched_switch:2' > \
+   	 set_ftrace_filter
+
+  The format is:
+
+    <function>:enable_event:<system>:<event>[:count]
+    <function>:disable_event:<system>:<event>[:count]
+
+  To remove the events commands:
+
+
+   echo '!try_to_wake_up:enable_event:sched:sched_switch:0' > \
+   	 set_ftrace_filter
+   echo '!schedule:disable_event:sched:sched_switch' > \
+   	 set_ftrace_filter
+
+- dump
+  When the function is hit, it will dump the contents of the ftrace
+  ring buffer to the console. This is useful if you need to debug
+  something, and want to dump the trace when a certain function
+  is hit. Perhaps its a function that is called before a tripple
+  fault happens and does not allow you to get a regular dump.
+
+- cpudump
+  When the function is hit, it will dump the contents of the ftrace
+  ring buffer for the current CPU to the console. Unlike the "dump"
+  command, it only prints out the contents of the ring buffer for the
+  CPU that executed the function that triggered the dump.
+
+trace_pipe
+----------
+
+The trace_pipe outputs the same content as the trace file, but
+the effect on the tracing is different. Every read from
+trace_pipe is consumed. This means that subsequent reads will be
+different. The trace is live.
+
+ # echo function > current_tracer
+ # cat trace_pipe > /tmp/trace.out &
+[1] 4153
+ # echo 1 > tracing_on
+ # usleep 1
+ # echo 0 > tracing_on
+ # cat trace
+# tracer: function
+#
+# entries-in-buffer/entries-written: 0/0   #P:4
+#
+#                              _-----=> irqs-off
+#                             / _----=> need-resched
+#                            | / _---=> hardirq/softirq
+#                            || / _--=> preempt-depth
+#                            ||| /     delay
+#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+#              | |       |   ||||       |         |
+
+ #
+ # cat /tmp/trace.out
+            bash-1994  [000] ....  5281.568961: mutex_unlock <-rb_simple_write
+            bash-1994  [000] ....  5281.568963: __mutex_unlock_slowpath <-mutex_unlock
+            bash-1994  [000] ....  5281.568963: __fsnotify_parent <-fsnotify_modify
+            bash-1994  [000] ....  5281.568964: fsnotify <-fsnotify_modify
+            bash-1994  [000] ....  5281.568964: __srcu_read_lock <-fsnotify
+            bash-1994  [000] ....  5281.568964: add_preempt_count <-__srcu_read_lock
+            bash-1994  [000] ...1  5281.568965: sub_preempt_count <-__srcu_read_lock
+            bash-1994  [000] ....  5281.568965: __srcu_read_unlock <-fsnotify
+            bash-1994  [000] ....  5281.568967: sys_dup2 <-system_call_fastpath
+
+
+Note, reading the trace_pipe file will block until more input is
+added.
+
+trace entries
+-------------
+
+Having too much or not enough data can be troublesome in
+diagnosing an issue in the kernel. The file buffer_size_kb is
+used to modify the size of the internal trace buffers. The
+number listed is the number of entries that can be recorded per
+CPU. To know the full size, multiply the number of possible CPUs
+with the number of entries.
+
+ # cat buffer_size_kb
+1408 (units kilobytes)
+
+Or simply read buffer_total_size_kb
+
+ # cat buffer_total_size_kb 
+5632
+
+To modify the buffer, simple echo in a number (in 1024 byte segments).
+
+ # echo 10000 > buffer_size_kb
+ # cat buffer_size_kb
+10000 (units kilobytes)
+
+It will try to allocate as much as possible. If you allocate too
+much, it can cause Out-Of-Memory to trigger.
+
+ # echo 1000000000000 > buffer_size_kb
+-bash: echo: write error: Cannot allocate memory
+ # cat buffer_size_kb
+85
+
+The per_cpu buffers can be changed individually as well:
+
+ # echo 10000 > per_cpu/cpu0/buffer_size_kb
+ # echo 100 > per_cpu/cpu1/buffer_size_kb
+
+When the per_cpu buffers are not the same, the buffer_size_kb
+at the top level will just show an X
+
+ # cat buffer_size_kb
+X
+
+This is where the buffer_total_size_kb is useful:
+
+ # cat buffer_total_size_kb 
+12916
+
+Writing to the top level buffer_size_kb will reset all the buffers
+to be the same again.
+
+Snapshot
+--------
+CONFIG_TRACER_SNAPSHOT makes a generic snapshot feature
+available to all non latency tracers. (Latency tracers which
+record max latency, such as "irqsoff" or "wakeup", can't use
+this feature, since those are already using the snapshot
+mechanism internally.)
+
+Snapshot preserves a current trace buffer at a particular point
+in time without stopping tracing. Ftrace swaps the current
+buffer with a spare buffer, and tracing continues in the new
+current (=previous spare) buffer.
+
+The following debugfs files in "tracing" are related to this
+feature:
+
+  snapshot:
+
+	This is used to take a snapshot and to read the output
+	of the snapshot. Echo 1 into this file to allocate a
+	spare buffer and to take a snapshot (swap), then read
+	the snapshot from this file in the same format as
+	"trace" (described above in the section "The File
+	System"). Both reads snapshot and tracing are executable
+	in parallel. When the spare buffer is allocated, echoing
+	0 frees it, and echoing else (positive) values clear the
+	snapshot contents.
+	More details are shown in the table below.
+
+	status\input  |     0      |     1      |    else    |
+	--------------+------------+------------+------------+
+	not allocated |(do nothing)| alloc+swap |(do nothing)|
+	--------------+------------+------------+------------+
+	allocated     |    free    |    swap    |   clear    |
+	--------------+------------+------------+------------+
+
+Here is an example of using the snapshot feature.
+
+ # echo 1 > events/sched/enable
+ # echo 1 > snapshot
+ # cat snapshot
+# tracer: nop
+#
+# entries-in-buffer/entries-written: 71/71   #P:8
+#
+#                              _-----=> irqs-off
+#                             / _----=> need-resched
+#                            | / _---=> hardirq/softirq
+#                            || / _--=> preempt-depth
+#                            ||| /     delay
+#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+#              | |       |   ||||       |         |
+          <idle>-0     [005] d...  2440.603828: sched_switch: prev_comm=swapper/5 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2242 next_prio=120
+           sleep-2242  [005] d...  2440.603846: sched_switch: prev_comm=snapshot-test-2 prev_pid=2242 prev_prio=120 prev_state=R ==> next_comm=kworker/5:1 next_pid=60 next_prio=120
+[...]
+          <idle>-0     [002] d...  2440.707230: sched_switch: prev_comm=swapper/2 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2229 next_prio=120
+
+ # cat trace
+# tracer: nop
+#
+# entries-in-buffer/entries-written: 77/77   #P:8
+#
+#                              _-----=> irqs-off
+#                             / _----=> need-resched
+#                            | / _---=> hardirq/softirq
+#                            || / _--=> preempt-depth
+#                            ||| /     delay
+#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+#              | |       |   ||||       |         |
+          <idle>-0     [007] d...  2440.707395: sched_switch: prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2243 next_prio=120
+ snapshot-test-2-2229  [002] d...  2440.707438: sched_switch: prev_comm=snapshot-test-2 prev_pid=2229 prev_prio=120 prev_state=S ==> next_comm=swapper/2 next_pid=0 next_prio=120
+[...]
+
+
+If you try to use this snapshot feature when current tracer is
+one of the latency tracers, you will get the following results.
+
+ # echo wakeup > current_tracer
+ # echo 1 > snapshot
+bash: echo: write error: Device or resource busy
+ # cat snapshot
+cat: snapshot: Device or resource busy
+
+
+Instances
+---------
+In the debugfs tracing directory is a directory called "instances".
+This directory can have new directories created inside of it using
+mkdir, and removing directories with rmdir. The directory created
+with mkdir in this directory will already contain files and other
+directories after it is created.
+
+ # mkdir instances/foo
+ # ls instances/foo
+buffer_size_kb  buffer_total_size_kb  events  free_buffer  per_cpu
+set_event  snapshot  trace  trace_clock  trace_marker  trace_options
+trace_pipe  tracing_on
+
+As you can see, the new directory looks similar to the tracing directory
+itself. In fact, it is very similar, except that the buffer and
+events are agnostic from the main director, or from any other
+instances that are created.
+
+The files in the new directory work just like the files with the
+same name in the tracing directory except the buffer that is used
+is a separate and new buffer. The files affect that buffer but do not
+affect the main buffer with the exception of trace_options. Currently,
+the trace_options affect all instances and the top level buffer
+the same, but this may change in future releases. That is, options
+may become specific to the instance they reside in.
+
+Notice that none of the function tracer files are there, nor is
+current_tracer and available_tracers. This is because the buffers
+can currently only have events enabled for them.
+
+ # mkdir instances/foo
+ # mkdir instances/bar
+ # mkdir instances/zoot
+ # echo 100000 > buffer_size_kb
+ # echo 1000 > instances/foo/buffer_size_kb
+ # echo 5000 > instances/bar/per_cpu/cpu1/buffer_size_kb
+ # echo function > current_trace
+ # echo 1 > instances/foo/events/sched/sched_wakeup/enable
+ # echo 1 > instances/foo/events/sched/sched_wakeup_new/enable
+ # echo 1 > instances/foo/events/sched/sched_switch/enable
+ # echo 1 > instances/bar/events/irq/enable
+ # echo 1 > instances/zoot/events/syscalls/enable
+ # cat trace_pipe
+CPU:2 [LOST 11745 EVENTS]
+            bash-2044  [002] .... 10594.481032: _raw_spin_lock_irqsave <-get_page_from_freelist
+            bash-2044  [002] d... 10594.481032: add_preempt_count <-_raw_spin_lock_irqsave
+            bash-2044  [002] d..1 10594.481032: __rmqueue <-get_page_from_freelist
+            bash-2044  [002] d..1 10594.481033: _raw_spin_unlock <-get_page_from_freelist
+            bash-2044  [002] d..1 10594.481033: sub_preempt_count <-_raw_spin_unlock
+            bash-2044  [002] d... 10594.481033: get_pageblock_flags_group <-get_pageblock_migratetype
+            bash-2044  [002] d... 10594.481034: __mod_zone_page_state <-get_page_from_freelist
+            bash-2044  [002] d... 10594.481034: zone_statistics <-get_page_from_freelist
+            bash-2044  [002] d... 10594.481034: __inc_zone_state <-zone_statistics
+            bash-2044  [002] d... 10594.481034: __inc_zone_state <-zone_statistics
+            bash-2044  [002] .... 10594.481035: arch_dup_task_struct <-copy_process
+[...]
+
+ # cat instances/foo/trace_pipe
+            bash-1998  [000] d..4   136.676759: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000
+            bash-1998  [000] dN.4   136.676760: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000
+          <idle>-0     [003] d.h3   136.676906: sched_wakeup: comm=rcu_preempt pid=9 prio=120 success=1 target_cpu=003
+          <idle>-0     [003] d..3   136.676909: sched_switch: prev_comm=swapper/3 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=rcu_preempt next_pid=9 next_prio=120
+     rcu_preempt-9     [003] d..3   136.676916: sched_switch: prev_comm=rcu_preempt prev_pid=9 prev_prio=120 prev_state=S ==> next_comm=swapper/3 next_pid=0 next_prio=120
+            bash-1998  [000] d..4   136.677014: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000
+            bash-1998  [000] dN.4   136.677016: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000
+            bash-1998  [000] d..3   136.677018: sched_switch: prev_comm=bash prev_pid=1998 prev_prio=120 prev_state=R+ ==> next_comm=kworker/0:1 next_pid=59 next_prio=120
+     kworker/0:1-59    [000] d..4   136.677022: sched_wakeup: comm=sshd pid=1995 prio=120 success=1 target_cpu=001
+     kworker/0:1-59    [000] d..3   136.677025: sched_switch: prev_comm=kworker/0:1 prev_pid=59 prev_prio=120 prev_state=S ==> next_comm=bash next_pid=1998 next_prio=120
+[...]
+
+ # cat instances/bar/trace_pipe
+     migration/1-14    [001] d.h3   138.732674: softirq_raise: vec=3 [action=NET_RX]
+          <idle>-0     [001] dNh3   138.732725: softirq_raise: vec=3 [action=NET_RX]
+            bash-1998  [000] d.h1   138.733101: softirq_raise: vec=1 [action=TIMER]
+            bash-1998  [000] d.h1   138.733102: softirq_raise: vec=9 [action=RCU]
+            bash-1998  [000] ..s2   138.733105: softirq_entry: vec=1 [action=TIMER]
+            bash-1998  [000] ..s2   138.733106: softirq_exit: vec=1 [action=TIMER]
+            bash-1998  [000] ..s2   138.733106: softirq_entry: vec=9 [action=RCU]
+            bash-1998  [000] ..s2   138.733109: softirq_exit: vec=9 [action=RCU]
+            sshd-1995  [001] d.h1   138.733278: irq_handler_entry: irq=21 name=uhci_hcd:usb4
+            sshd-1995  [001] d.h1   138.733280: irq_handler_exit: irq=21 ret=unhandled
+            sshd-1995  [001] d.h1   138.733281: irq_handler_entry: irq=21 name=eth0
+            sshd-1995  [001] d.h1   138.733283: irq_handler_exit: irq=21 ret=handled
+[...]
+
+ # cat instances/zoot/trace
+# tracer: nop
+#
+# entries-in-buffer/entries-written: 18996/18996   #P:4
+#
+#                              _-----=> irqs-off
+#                             / _----=> need-resched
+#                            | / _---=> hardirq/softirq
+#                            || / _--=> preempt-depth
+#                            ||| /     delay
+#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+#              | |       |   ||||       |         |
+            bash-1998  [000] d...   140.733501: sys_write -> 0x2
+            bash-1998  [000] d...   140.733504: sys_dup2(oldfd: a, newfd: 1)
+            bash-1998  [000] d...   140.733506: sys_dup2 -> 0x1
+            bash-1998  [000] d...   140.733508: sys_fcntl(fd: a, cmd: 1, arg: 0)
+            bash-1998  [000] d...   140.733509: sys_fcntl -> 0x1
+            bash-1998  [000] d...   140.733510: sys_close(fd: a)
+            bash-1998  [000] d...   140.733510: sys_close -> 0x0
+            bash-1998  [000] d...   140.733514: sys_rt_sigprocmask(how: 0, nset: 0, oset: 6e2768, sigsetsize: 8)
+            bash-1998  [000] d...   140.733515: sys_rt_sigprocmask -> 0x0
+            bash-1998  [000] d...   140.733516: sys_rt_sigaction(sig: 2, act: 7fff718846f0, oact: 7fff71884650, sigsetsize: 8)
+            bash-1998  [000] d...   140.733516: sys_rt_sigaction -> 0x0
+
+You can see that the trace of the top most trace buffer shows only
+the function tracing. The foo instance displays wakeups and task
+switches.
+
+To remove the instances, simply delete their directories:
+
+ # rmdir instances/foo
+ # rmdir instances/bar
+ # rmdir instances/zoot
+
+Note, if a process has a trace file open in one of the instance
+directories, the rmdir will fail with EBUSY.
+
+
+Stack trace
+-----------
+Since the kernel has a fixed sized stack, it is important not to
+waste it in functions. A kernel developer must be conscience of
+what they allocate on the stack. If they add too much, the system
+can be in danger of a stack overflow, and corruption will occur,
+usually leading to a system panic.
+
+There are some tools that check this, usually with interrupts
+periodically checking usage. But if you can perform a check
+at every function call that will become very useful. As ftrace provides
+a function tracer, it makes it convenient to check the stack size
+at every function call. This is enabled via the stack tracer.
+
+CONFIG_STACK_TRACER enables the ftrace stack tracing functionality.
+To enable it, write a '1' into /proc/sys/kernel/stack_tracer_enabled.
+
+ # echo 1 > /proc/sys/kernel/stack_tracer_enabled
+
+You can also enable it from the kernel command line to trace
+the stack size of the kernel during boot up, by adding "stacktrace"
+to the kernel command line parameter.
+
+After running it for a few minutes, the output looks like:
+
+ # cat stack_max_size
+2928
+
+ # cat stack_trace
+        Depth    Size   Location    (18 entries)
+        -----    ----   --------
+  0)     2928     224   update_sd_lb_stats+0xbc/0x4ac
+  1)     2704     160   find_busiest_group+0x31/0x1f1
+  2)     2544     256   load_balance+0xd9/0x662
+  3)     2288      80   idle_balance+0xbb/0x130
+  4)     2208     128   __schedule+0x26e/0x5b9
+  5)     2080      16   schedule+0x64/0x66
+  6)     2064     128   schedule_timeout+0x34/0xe0
+  7)     1936     112   wait_for_common+0x97/0xf1
+  8)     1824      16   wait_for_completion+0x1d/0x1f
+  9)     1808     128   flush_work+0xfe/0x119
+ 10)     1680      16   tty_flush_to_ldisc+0x1e/0x20
+ 11)     1664      48   input_available_p+0x1d/0x5c
+ 12)     1616      48   n_tty_poll+0x6d/0x134
+ 13)     1568      64   tty_poll+0x64/0x7f
+ 14)     1504     880   do_select+0x31e/0x511
+ 15)      624     400   core_sys_select+0x177/0x216
+ 16)      224      96   sys_select+0x91/0xb9
+ 17)      128     128   system_call_fastpath+0x16/0x1b
+
+Note, if -mfentry is being used by gcc, functions get traced before
+they set up the stack frame. This means that leaf level functions
+are not tested by the stack tracer when -mfentry is used.
+
+Currently, -mfentry is used by gcc 4.6.0 and above on x86 only.
+
+---------
+
+More details can be found in the source code, in the
+kernel/trace/*.c files.
diff --git a/Documentation/trace/function-graph-fold.vim b/Documentation/trace/function-graph-fold.vim
new file mode 100644
index 000000000..0544b504c
--- /dev/null
+++ b/Documentation/trace/function-graph-fold.vim
@@ -0,0 +1,42 @@
+" Enable folding for ftrace function_graph traces.
+"
+" To use, :source this file while viewing a function_graph trace, or use vim's
+" -S option to load from the command-line together with a trace.  You can then
+" use the usual vim fold commands, such as "za", to open and close nested
+" functions.  While closed, a fold will show the total time taken for a call,
+" as would normally appear on the line with the closing brace.  Folded
+" functions will not include finish_task_switch(), so folding should remain
+" relatively sane even through a context switch.
+"
+" Note that this will almost certainly only work well with a
+" single-CPU trace (e.g. trace-cmd report --cpu 1).
+
+function! FunctionGraphFoldExpr(lnum)
+  let line = getline(a:lnum)
+  if line[-1:] == '{'
+    if line =~ 'finish_task_switch() {$'
+      return '>1'
+    endif
+    return 'a1'
+  elseif line[-1:] == '}'
+    return 's1'
+  else
+    return '='
+  endif
+endfunction
+
+function! FunctionGraphFoldText()
+  let s = split(getline(v:foldstart), '|', 1)
+  if getline(v:foldend+1) =~ 'finish_task_switch() {$'
+    let s[2] = ' task switch  '
+  else
+    let e = split(getline(v:foldend), '|', 1)
+    let s[2] = e[2]
+  endif
+  return join(s, '|')
+endfunction
+
+setlocal foldexpr=FunctionGraphFoldExpr(v:lnum)
+setlocal foldtext=FunctionGraphFoldText()
+setlocal foldcolumn=12
+setlocal foldmethod=expr
diff --git a/Documentation/trace/kprobetrace.txt b/Documentation/trace/kprobetrace.txt
new file mode 100644
index 000000000..d68ea5fc8
--- /dev/null
+++ b/Documentation/trace/kprobetrace.txt
@@ -0,0 +1,172 @@
+                        Kprobe-based Event Tracing
+                        ==========================
+
+                 Documentation is written by Masami Hiramatsu
+
+
+Overview
+--------
+These events are similar to tracepoint based events. Instead of Tracepoint,
+this is based on kprobes (kprobe and kretprobe). So it can probe wherever
+kprobes can probe (this means, all functions body except for __kprobes
+functions). Unlike the Tracepoint based event, this can be added and removed
+dynamically, on the fly.
+
+To enable this feature, build your kernel with CONFIG_KPROBE_EVENT=y.
+
+Similar to the events tracer, this doesn't need to be activated via
+current_tracer. Instead of that, add probe points via
+/sys/kernel/debug/tracing/kprobe_events, and enable it via
+/sys/kernel/debug/tracing/events/kprobes/<EVENT>/enabled.
+
+
+Synopsis of kprobe_events
+-------------------------
+  p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS]	: Set a probe
+  r[:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS]		: Set a return probe
+  -:[GRP/]EVENT						: Clear a probe
+
+ GRP		: Group name. If omitted, use "kprobes" for it.
+ EVENT		: Event name. If omitted, the event name is generated
+		  based on SYM+offs or MEMADDR.
+ MOD		: Module name which has given SYM.
+ SYM[+offs]	: Symbol+offset where the probe is inserted.
+ MEMADDR	: Address where the probe is inserted.
+
+ FETCHARGS	: Arguments. Each probe can have up to 128 args.
+  %REG		: Fetch register REG
+  @ADDR		: Fetch memory at ADDR (ADDR should be in kernel)
+  @SYM[+|-offs]	: Fetch memory at SYM +|- offs (SYM should be a data symbol)
+  $stackN	: Fetch Nth entry of stack (N >= 0)
+  $stack	: Fetch stack address.
+  $retval	: Fetch return value.(*)
+  +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
+  NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
+  FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
+		  (u8/u16/u32/u64/s8/s16/s32/s64), "string" and bitfield
+		  are supported.
+
+  (*) only for return probe.
+  (**) this is useful for fetching a field of data structures.
+
+Types
+-----
+Several types are supported for fetch-args. Kprobe tracer will access memory
+by given type. Prefix 's' and 'u' means those types are signed and unsigned
+respectively. Traced arguments are shown in decimal (signed) or hex (unsigned).
+String type is a special type, which fetches a "null-terminated" string from
+kernel space. This means it will fail and store NULL if the string container
+has been paged out.
+Bitfield is another special type, which takes 3 parameters, bit-width, bit-
+offset, and container-size (usually 32). The syntax is;
+
+ b<bit-width>@<bit-offset>/<container-size>
+
+
+Per-Probe Event Filtering
+-------------------------
+ Per-probe event filtering feature allows you to set different filter on each
+probe and gives you what arguments will be shown in trace buffer. If an event
+name is specified right after 'p:' or 'r:' in kprobe_events, it adds an event
+under tracing/events/kprobes/<EVENT>, at the directory you can see 'id',
+'enabled', 'format' and 'filter'.
+
+enabled:
+  You can enable/disable the probe by writing 1 or 0 on it.
+
+format:
+  This shows the format of this probe event.
+
+filter:
+  You can write filtering rules of this event.
+
+id:
+  This shows the id of this probe event.
+
+
+Event Profiling
+---------------
+ You can check the total number of probe hits and probe miss-hits via
+/sys/kernel/debug/tracing/kprobe_profile.
+ The first column is event name, the second is the number of probe hits,
+the third is the number of probe miss-hits.
+
+
+Usage examples
+--------------
+To add a probe as a new event, write a new definition to kprobe_events
+as below.
+
+  echo 'p:myprobe do_sys_open dfd=%ax filename=%dx flags=%cx mode=+4($stack)' > /sys/kernel/debug/tracing/kprobe_events
+
+ This sets a kprobe on the top of do_sys_open() function with recording
+1st to 4th arguments as "myprobe" event. Note, which register/stack entry is
+assigned to each function argument depends on arch-specific ABI. If you unsure
+the ABI, please try to use probe subcommand of perf-tools (you can find it
+under tools/perf/).
+As this example shows, users can choose more familiar names for each arguments.
+
+  echo 'r:myretprobe do_sys_open $retval' >> /sys/kernel/debug/tracing/kprobe_events
+
+ This sets a kretprobe on the return point of do_sys_open() function with
+recording return value as "myretprobe" event.
+ You can see the format of these events via
+/sys/kernel/debug/tracing/events/kprobes/<EVENT>/format.
+
+  cat /sys/kernel/debug/tracing/events/kprobes/myprobe/format
+name: myprobe
+ID: 780
+format:
+        field:unsigned short common_type;       offset:0;       size:2; signed:0;
+        field:unsigned char common_flags;       offset:2;       size:1; signed:0;
+        field:unsigned char common_preempt_count;       offset:3; size:1;signed:0;
+        field:int common_pid;   offset:4;       size:4; signed:1;
+
+        field:unsigned long __probe_ip; offset:12;      size:4; signed:0;
+        field:int __probe_nargs;        offset:16;      size:4; signed:1;
+        field:unsigned long dfd;        offset:20;      size:4; signed:0;
+        field:unsigned long filename;   offset:24;      size:4; signed:0;
+        field:unsigned long flags;      offset:28;      size:4; signed:0;
+        field:unsigned long mode;       offset:32;      size:4; signed:0;
+
+
+print fmt: "(%lx) dfd=%lx filename=%lx flags=%lx mode=%lx", REC->__probe_ip,
+REC->dfd, REC->filename, REC->flags, REC->mode
+
+ You can see that the event has 4 arguments as in the expressions you specified.
+
+  echo > /sys/kernel/debug/tracing/kprobe_events
+
+ This clears all probe points.
+
+ Or,
+
+  echo -:myprobe >> kprobe_events
+
+ This clears probe points selectively.
+
+ Right after definition, each event is disabled by default. For tracing these
+events, you need to enable it.
+
+  echo 1 > /sys/kernel/debug/tracing/events/kprobes/myprobe/enable
+  echo 1 > /sys/kernel/debug/tracing/events/kprobes/myretprobe/enable
+
+ And you can see the traced information via /sys/kernel/debug/tracing/trace.
+
+  cat /sys/kernel/debug/tracing/trace
+# tracer: nop
+#
+#           TASK-PID    CPU#    TIMESTAMP  FUNCTION
+#              | |       |          |         |
+           <...>-1447  [001] 1038282.286875: myprobe: (do_sys_open+0x0/0xd6) dfd=3 filename=7fffd1ec4440 flags=8000 mode=0
+           <...>-1447  [001] 1038282.286878: myretprobe: (sys_openat+0xc/0xe <- do_sys_open) $retval=fffffffffffffffe
+           <...>-1447  [001] 1038282.286885: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=40413c flags=8000 mode=1b6
+           <...>-1447  [001] 1038282.286915: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3
+           <...>-1447  [001] 1038282.286969: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=4041c6 flags=98800 mode=10
+           <...>-1447  [001] 1038282.286976: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3
+
+
+ Each line shows when the kernel hits an event, and <- SYMBOL means kernel
+returns from SYMBOL(e.g. "sys_open+0x1b/0x1d <- do_sys_open" means kernel
+returns from do_sys_open to sys_open+0x1b).
+
diff --git a/Documentation/trace/mmiotrace.txt b/Documentation/trace/mmiotrace.txt
new file mode 100644
index 000000000..664e7386d
--- /dev/null
+++ b/Documentation/trace/mmiotrace.txt
@@ -0,0 +1,164 @@
+		In-kernel memory-mapped I/O tracing
+
+
+Home page and links to optional user space tools:
+
+	http://nouveau.freedesktop.org/wiki/MmioTrace
+
+MMIO tracing was originally developed by Intel around 2003 for their Fault
+Injection Test Harness. In Dec 2006 - Jan 2007, using the code from Intel,
+Jeff Muizelaar created a tool for tracing MMIO accesses with the Nouveau
+project in mind. Since then many people have contributed.
+
+Mmiotrace was built for reverse engineering any memory-mapped IO device with
+the Nouveau project as the first real user. Only x86 and x86_64 architectures
+are supported.
+
+Out-of-tree mmiotrace was originally modified for mainline inclusion and
+ftrace framework by Pekka Paalanen <pq@iki.fi>.
+
+
+Preparation
+-----------
+
+Mmiotrace feature is compiled in by the CONFIG_MMIOTRACE option. Tracing is
+disabled by default, so it is safe to have this set to yes. SMP systems are
+supported, but tracing is unreliable and may miss events if more than one CPU
+is on-line, therefore mmiotrace takes all but one CPU off-line during run-time
+activation. You can re-enable CPUs by hand, but you have been warned, there
+is no way to automatically detect if you are losing events due to CPUs racing.
+
+
+Usage Quick Reference
+---------------------
+
+$ mount -t debugfs debugfs /sys/kernel/debug
+$ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer
+$ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt &
+Start X or whatever.
+$ echo "X is up" > /sys/kernel/debug/tracing/trace_marker
+$ echo nop > /sys/kernel/debug/tracing/current_tracer
+Check for lost events.
+
+
+Usage
+-----
+
+Make sure debugfs is mounted to /sys/kernel/debug.
+If not (requires root privileges):
+$ mount -t debugfs debugfs /sys/kernel/debug
+
+Check that the driver you are about to trace is not loaded.
+
+Activate mmiotrace (requires root privileges):
+$ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer
+
+Start storing the trace:
+$ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt &
+The 'cat' process should stay running (sleeping) in the background.
+
+Load the driver you want to trace and use it. Mmiotrace will only catch MMIO
+accesses to areas that are ioremapped while mmiotrace is active.
+
+During tracing you can place comments (markers) into the trace by
+$ echo "X is up" > /sys/kernel/debug/tracing/trace_marker
+This makes it easier to see which part of the (huge) trace corresponds to
+which action. It is recommended to place descriptive markers about what you
+do.
+
+Shut down mmiotrace (requires root privileges):
+$ echo nop > /sys/kernel/debug/tracing/current_tracer
+The 'cat' process exits. If it does not, kill it by issuing 'fg' command and
+pressing ctrl+c.
+
+Check that mmiotrace did not lose events due to a buffer filling up. Either
+$ grep -i lost mydump.txt
+which tells you exactly how many events were lost, or use
+$ dmesg
+to view your kernel log and look for "mmiotrace has lost events" warning. If
+events were lost, the trace is incomplete. You should enlarge the buffers and
+try again. Buffers are enlarged by first seeing how large the current buffers
+are:
+$ cat /sys/kernel/debug/tracing/buffer_size_kb
+gives you a number. Approximately double this number and write it back, for
+instance:
+$ echo 128000 > /sys/kernel/debug/tracing/buffer_size_kb
+Then start again from the top.
+
+If you are doing a trace for a driver project, e.g. Nouveau, you should also
+do the following before sending your results:
+$ lspci -vvv > lspci.txt
+$ dmesg > dmesg.txt
+$ tar zcf pciid-nick-mmiotrace.tar.gz mydump.txt lspci.txt dmesg.txt
+and then send the .tar.gz file. The trace compresses considerably. Replace
+"pciid" and "nick" with the PCI ID or model name of your piece of hardware
+under investigation and your nickname.
+
+
+How Mmiotrace Works
+-------------------
+
+Access to hardware IO-memory is gained by mapping addresses from PCI bus by
+calling one of the ioremap_*() functions. Mmiotrace is hooked into the
+__ioremap() function and gets called whenever a mapping is created. Mapping is
+an event that is recorded into the trace log. Note that ISA range mappings
+are not caught, since the mapping always exists and is returned directly.
+
+MMIO accesses are recorded via page faults. Just before __ioremap() returns,
+the mapped pages are marked as not present. Any access to the pages causes a
+fault. The page fault handler calls mmiotrace to handle the fault. Mmiotrace
+marks the page present, sets TF flag to achieve single stepping and exits the
+fault handler. The instruction that faulted is executed and debug trap is
+entered. Here mmiotrace again marks the page as not present. The instruction
+is decoded to get the type of operation (read/write), data width and the value
+read or written. These are stored to the trace log.
+
+Setting the page present in the page fault handler has a race condition on SMP
+machines. During the single stepping other CPUs may run freely on that page
+and events can be missed without a notice. Re-enabling other CPUs during
+tracing is discouraged.
+
+
+Trace Log Format
+----------------
+
+The raw log is text and easily filtered with e.g. grep and awk. One record is
+one line in the log. A record starts with a keyword, followed by keyword-
+dependent arguments. Arguments are separated by a space, or continue until the
+end of line. The format for version 20070824 is as follows:
+
+Explanation	Keyword	Space-separated arguments
+---------------------------------------------------------------------------
+
+read event	R	width, timestamp, map id, physical, value, PC, PID
+write event	W	width, timestamp, map id, physical, value, PC, PID
+ioremap event	MAP	timestamp, map id, physical, virtual, length, PC, PID
+iounmap event	UNMAP	timestamp, map id, PC, PID
+marker		MARK	timestamp, text
+version		VERSION	the string "20070824"
+info for reader	LSPCI	one line from lspci -v
+PCI address map	PCIDEV	space-separated /proc/bus/pci/devices data
+unk. opcode	UNKNOWN	timestamp, map id, physical, data, PC, PID
+
+Timestamp is in seconds with decimals. Physical is a PCI bus address, virtual
+is a kernel virtual address. Width is the data width in bytes and value is the
+data value. Map id is an arbitrary id number identifying the mapping that was
+used in an operation. PC is the program counter and PID is process id. PC is
+zero if it is not recorded. PID is always zero as tracing MMIO accesses
+originating in user space memory is not yet supported.
+
+For instance, the following awk filter will pass all 32-bit writes that target
+physical addresses in the range [0xfb73ce40, 0xfb800000[
+
+$ awk '/W 4 / { adr=strtonum($5); if (adr >= 0xfb73ce40 &&
+adr < 0xfb800000) print; }'
+
+
+Tools for Developers
+--------------------
+
+The user space tools include utilities for:
+- replacing numeric addresses and values with hardware register names
+- replaying MMIO logs, i.e., re-executing the recorded writes
+
+
diff --git a/Documentation/trace/postprocess/trace-pagealloc-postprocess.pl b/Documentation/trace/postprocess/trace-pagealloc-postprocess.pl
new file mode 100644
index 000000000..0a120aae3
--- /dev/null
+++ b/Documentation/trace/postprocess/trace-pagealloc-postprocess.pl
@@ -0,0 +1,418 @@
+#!/usr/bin/perl
+# This is a POC (proof of concept or piece of crap, take your pick) for reading the
+# text representation of trace output related to page allocation. It makes an attempt
+# to extract some high-level information on what is going on. The accuracy of the parser
+# may vary considerably
+#
+# Example usage: trace-pagealloc-postprocess.pl < /sys/kernel/debug/tracing/trace_pipe
+# other options
+#   --prepend-parent	Report on the parent proc and PID
+#   --read-procstat	If the trace lacks process info, get it from /proc
+#   --ignore-pid	Aggregate processes of the same name together
+#
+# Copyright (c) IBM Corporation 2009
+# Author: Mel Gorman <mel@csn.ul.ie>
+use strict;
+use Getopt::Long;
+
+# Tracepoint events
+use constant MM_PAGE_ALLOC		=> 1;
+use constant MM_PAGE_FREE		=> 2;
+use constant MM_PAGE_FREE_BATCHED	=> 3;
+use constant MM_PAGE_PCPU_DRAIN		=> 4;
+use constant MM_PAGE_ALLOC_ZONE_LOCKED	=> 5;
+use constant MM_PAGE_ALLOC_EXTFRAG	=> 6;
+use constant EVENT_UNKNOWN		=> 7;
+
+# Constants used to track state
+use constant STATE_PCPU_PAGES_DRAINED	=> 8;
+use constant STATE_PCPU_PAGES_REFILLED	=> 9;
+
+# High-level events extrapolated from tracepoints
+use constant HIGH_PCPU_DRAINS		=> 10;
+use constant HIGH_PCPU_REFILLS		=> 11;
+use constant HIGH_EXT_FRAGMENT		=> 12;
+use constant HIGH_EXT_FRAGMENT_SEVERE	=> 13;
+use constant HIGH_EXT_FRAGMENT_MODERATE	=> 14;
+use constant HIGH_EXT_FRAGMENT_CHANGED	=> 15;
+
+my %perprocesspid;
+my %perprocess;
+my $opt_ignorepid;
+my $opt_read_procstat;
+my $opt_prepend_parent;
+
+# Catch sigint and exit on request
+my $sigint_report = 0;
+my $sigint_exit = 0;
+my $sigint_pending = 0;
+my $sigint_received = 0;
+sub sigint_handler {
+	my $current_time = time;
+	if ($current_time - 2 > $sigint_received) {
+		print "SIGINT received, report pending. Hit ctrl-c again to exit\n";
+		$sigint_report = 1;
+	} else {
+		if (!$sigint_exit) {
+			print "Second SIGINT received quickly, exiting\n";
+		}
+		$sigint_exit++;
+	}
+
+	if ($sigint_exit > 3) {
+		print "Many SIGINTs received, exiting now without report\n";
+		exit;
+	}
+
+	$sigint_received = $current_time;
+	$sigint_pending = 1;
+}
+$SIG{INT} = "sigint_handler";
+
+# Parse command line options
+GetOptions(
+	'ignore-pid'	 =>	\$opt_ignorepid,
+	'read-procstat'	 =>	\$opt_read_procstat,
+	'prepend-parent' =>	\$opt_prepend_parent,
+);
+
+# Defaults for dynamically discovered regex's
+my $regex_fragdetails_default = 'page=([0-9a-f]*) pfn=([0-9]*) alloc_order=([-0-9]*) fallback_order=([-0-9]*) pageblock_order=([-0-9]*) alloc_migratetype=([-0-9]*) fallback_migratetype=([-0-9]*) fragmenting=([-0-9]) change_ownership=([-0-9])';
+
+# Dyanically discovered regex
+my $regex_fragdetails;
+
+# Static regex used. Specified like this for readability and for use with /o
+#                      (process_pid)     (cpus      )   ( time  )   (tpoint    ) (details)
+my $regex_traceevent = '\s*([a-zA-Z0-9-]*)\s*(\[[0-9]*\])\s*([0-9.]*):\s*([a-zA-Z_]*):\s*(.*)';
+my $regex_statname = '[-0-9]*\s\((.*)\).*';
+my $regex_statppid = '[-0-9]*\s\(.*\)\s[A-Za-z]\s([0-9]*).*';
+
+sub generate_traceevent_regex {
+	my $event = shift;
+	my $default = shift;
+	my $regex;
+
+	# Read the event format or use the default
+	if (!open (FORMAT, "/sys/kernel/debug/tracing/events/$event/format")) {
+		$regex = $default;
+	} else {
+		my $line;
+		while (!eof(FORMAT)) {
+			$line = <FORMAT>;
+			if ($line =~ /^print fmt:\s"(.*)",.*/) {
+				$regex = $1;
+				$regex =~ s/%p/\([0-9a-f]*\)/g;
+				$regex =~ s/%d/\([-0-9]*\)/g;
+				$regex =~ s/%lu/\([0-9]*\)/g;
+			}
+		}
+	}
+
+	# Verify fields are in the right order
+	my $tuple;
+	foreach $tuple (split /\s/, $regex) {
+		my ($key, $value) = split(/=/, $tuple);
+		my $expected = shift;
+		if ($key ne $expected) {
+			print("WARNING: Format not as expected '$key' != '$expected'");
+			$regex =~ s/$key=\((.*)\)/$key=$1/;
+		}
+	}
+
+	if (defined shift) {
+		die("Fewer fields than expected in format");
+	}
+
+	return $regex;
+}
+$regex_fragdetails = generate_traceevent_regex("kmem/mm_page_alloc_extfrag",
+			$regex_fragdetails_default,
+			"page", "pfn",
+			"alloc_order", "fallback_order", "pageblock_order",
+			"alloc_migratetype", "fallback_migratetype",
+			"fragmenting", "change_ownership");
+
+sub read_statline($) {
+	my $pid = $_[0];
+	my $statline;
+
+	if (open(STAT, "/proc/$pid/stat")) {
+		$statline = <STAT>;
+		close(STAT);
+	}
+
+	if ($statline eq '') {
+		$statline = "-1 (UNKNOWN_PROCESS_NAME) R 0";
+	}
+
+	return $statline;
+}
+
+sub guess_process_pid($$) {
+	my $pid = $_[0];
+	my $statline = $_[1];
+
+	if ($pid == 0) {
+		return "swapper-0";
+	}
+
+	if ($statline !~ /$regex_statname/o) {
+		die("Failed to math stat line for process name :: $statline");
+	}
+	return "$1-$pid";
+}
+
+sub parent_info($$) {
+	my $pid = $_[0];
+	my $statline = $_[1];
+	my $ppid;
+
+	if ($pid == 0) {
+		return "NOPARENT-0";
+	}
+
+	if ($statline !~ /$regex_statppid/o) {
+		die("Failed to match stat line process ppid:: $statline");
+	}
+
+	# Read the ppid stat line
+	$ppid = $1;
+	return guess_process_pid($ppid, read_statline($ppid));
+}
+
+sub process_events {
+	my $traceevent;
+	my $process_pid;
+	my $cpus;
+	my $timestamp;
+	my $tracepoint;
+	my $details;
+	my $statline;
+
+	# Read each line of the event log
+EVENT_PROCESS:
+	while ($traceevent = <STDIN>) {
+		if ($traceevent =~ /$regex_traceevent/o) {
+			$process_pid = $1;
+			$tracepoint = $4;
+
+			if ($opt_read_procstat || $opt_prepend_parent) {
+				$process_pid =~ /(.*)-([0-9]*)$/;
+				my $process = $1;
+				my $pid = $2;
+
+				$statline = read_statline($pid);
+
+				if ($opt_read_procstat && $process eq '') {
+					$process_pid = guess_process_pid($pid, $statline);
+				}
+
+				if ($opt_prepend_parent) {
+					$process_pid = parent_info($pid, $statline) . " :: $process_pid";
+				}
+			}
+
+			# Unnecessary in this script. Uncomment if required
+			# $cpus = $2;
+			# $timestamp = $3;
+		} else {
+			next;
+		}
+
+		# Perl Switch() sucks majorly
+		if ($tracepoint eq "mm_page_alloc") {
+			$perprocesspid{$process_pid}->{MM_PAGE_ALLOC}++;
+		} elsif ($tracepoint eq "mm_page_free") {
+			$perprocesspid{$process_pid}->{MM_PAGE_FREE}++
+		} elsif ($tracepoint eq "mm_page_free_batched") {
+			$perprocesspid{$process_pid}->{MM_PAGE_FREE_BATCHED}++;
+		} elsif ($tracepoint eq "mm_page_pcpu_drain") {
+			$perprocesspid{$process_pid}->{MM_PAGE_PCPU_DRAIN}++;
+			$perprocesspid{$process_pid}->{STATE_PCPU_PAGES_DRAINED}++;
+		} elsif ($tracepoint eq "mm_page_alloc_zone_locked") {
+			$perprocesspid{$process_pid}->{MM_PAGE_ALLOC_ZONE_LOCKED}++;
+			$perprocesspid{$process_pid}->{STATE_PCPU_PAGES_REFILLED}++;
+		} elsif ($tracepoint eq "mm_page_alloc_extfrag") {
+
+			# Extract the details of the event now
+			$details = $5;
+
+			my ($page, $pfn);
+			my ($alloc_order, $fallback_order, $pageblock_order);
+			my ($alloc_migratetype, $fallback_migratetype);
+			my ($fragmenting, $change_ownership);
+
+			if ($details !~ /$regex_fragdetails/o) {
+				print "WARNING: Failed to parse mm_page_alloc_extfrag as expected\n";
+				next;
+			}
+
+			$perprocesspid{$process_pid}->{MM_PAGE_ALLOC_EXTFRAG}++;
+			$page = $1;
+			$pfn = $2;
+			$alloc_order = $3;
+			$fallback_order = $4;
+			$pageblock_order = $5;
+			$alloc_migratetype = $6;
+			$fallback_migratetype = $7;
+			$fragmenting = $8;
+			$change_ownership = $9;
+
+			if ($fragmenting) {
+				$perprocesspid{$process_pid}->{HIGH_EXT_FRAG}++;
+				if ($fallback_order <= 3) {
+					$perprocesspid{$process_pid}->{HIGH_EXT_FRAGMENT_SEVERE}++;
+				} else {
+					$perprocesspid{$process_pid}->{HIGH_EXT_FRAGMENT_MODERATE}++;
+				}
+			}
+			if ($change_ownership) {
+				$perprocesspid{$process_pid}->{HIGH_EXT_FRAGMENT_CHANGED}++;
+			}
+		} else {
+			$perprocesspid{$process_pid}->{EVENT_UNKNOWN}++;
+		}
+
+		# Catch a full pcpu drain event
+		if ($perprocesspid{$process_pid}->{STATE_PCPU_PAGES_DRAINED} &&
+				$tracepoint ne "mm_page_pcpu_drain") {
+
+			$perprocesspid{$process_pid}->{HIGH_PCPU_DRAINS}++;
+			$perprocesspid{$process_pid}->{STATE_PCPU_PAGES_DRAINED} = 0;
+		}
+
+		# Catch a full pcpu refill event
+		if ($perprocesspid{$process_pid}->{STATE_PCPU_PAGES_REFILLED} &&
+				$tracepoint ne "mm_page_alloc_zone_locked") {
+			$perprocesspid{$process_pid}->{HIGH_PCPU_REFILLS}++;
+			$perprocesspid{$process_pid}->{STATE_PCPU_PAGES_REFILLED} = 0;
+		}
+
+		if ($sigint_pending) {
+			last EVENT_PROCESS;
+		}
+	}
+}
+
+sub dump_stats {
+	my $hashref = shift;
+	my %stats = %$hashref;
+
+	# Dump per-process stats
+	my $process_pid;
+	my $max_strlen = 0;
+
+	# Get the maximum process name
+	foreach $process_pid (keys %perprocesspid) {
+		my $len = length($process_pid);
+		if ($len > $max_strlen) {
+			$max_strlen = $len;
+		}
+	}
+	$max_strlen += 2;
+
+	printf("\n");
+	printf("%-" . $max_strlen . "s %8s %10s   %8s %8s   %8s %8s %8s   %8s %8s %8s %8s %8s %8s\n",
+		"Process", "Pages",  "Pages",      "Pages", "Pages", "PCPU",  "PCPU",   "PCPU",    "Fragment",  "Fragment", "MigType", "Fragment", "Fragment", "Unknown");
+	printf("%-" . $max_strlen . "s %8s %10s   %8s %8s   %8s %8s %8s   %8s %8s %8s %8s %8s %8s\n",
+		"details", "allocd", "allocd",     "freed", "freed", "pages", "drains", "refills", "Fallback", "Causing",   "Changed", "Severe", "Moderate", "");
+
+	printf("%-" . $max_strlen . "s %8s %10s   %8s %8s   %8s %8s %8s   %8s %8s %8s %8s %8s %8s\n",
+		"",        "",       "under lock", "direct", "pagevec", "drain", "", "", "", "", "", "", "", "");
+
+	foreach $process_pid (keys %stats) {
+		# Dump final aggregates
+		if ($stats{$process_pid}->{STATE_PCPU_PAGES_DRAINED}) {
+			$stats{$process_pid}->{HIGH_PCPU_DRAINS}++;
+			$stats{$process_pid}->{STATE_PCPU_PAGES_DRAINED} = 0;
+		}
+		if ($stats{$process_pid}->{STATE_PCPU_PAGES_REFILLED}) {
+			$stats{$process_pid}->{HIGH_PCPU_REFILLS}++;
+			$stats{$process_pid}->{STATE_PCPU_PAGES_REFILLED} = 0;
+		}
+
+		printf("%-" . $max_strlen . "s %8d %10d   %8d %8d   %8d %8d %8d   %8d %8d %8d %8d %8d %8d\n",
+			$process_pid,
+			$stats{$process_pid}->{MM_PAGE_ALLOC},
+			$stats{$process_pid}->{MM_PAGE_ALLOC_ZONE_LOCKED},
+			$stats{$process_pid}->{MM_PAGE_FREE},
+			$stats{$process_pid}->{MM_PAGE_FREE_BATCHED},
+			$stats{$process_pid}->{MM_PAGE_PCPU_DRAIN},
+			$stats{$process_pid}->{HIGH_PCPU_DRAINS},
+			$stats{$process_pid}->{HIGH_PCPU_REFILLS},
+			$stats{$process_pid}->{MM_PAGE_ALLOC_EXTFRAG},
+			$stats{$process_pid}->{HIGH_EXT_FRAG},
+			$stats{$process_pid}->{HIGH_EXT_FRAGMENT_CHANGED},
+			$stats{$process_pid}->{HIGH_EXT_FRAGMENT_SEVERE},
+			$stats{$process_pid}->{HIGH_EXT_FRAGMENT_MODERATE},
+			$stats{$process_pid}->{EVENT_UNKNOWN});
+	}
+}
+
+sub aggregate_perprocesspid() {
+	my $process_pid;
+	my $process;
+	undef %perprocess;
+
+	foreach $process_pid (keys %perprocesspid) {
+		$process = $process_pid;
+		$process =~ s/-([0-9])*$//;
+		if ($process eq '') {
+			$process = "NO_PROCESS_NAME";
+		}
+
+		$perprocess{$process}->{MM_PAGE_ALLOC} += $perprocesspid{$process_pid}->{MM_PAGE_ALLOC};
+		$perprocess{$process}->{MM_PAGE_ALLOC_ZONE_LOCKED} += $perprocesspid{$process_pid}->{MM_PAGE_ALLOC_ZONE_LOCKED};
+		$perprocess{$process}->{MM_PAGE_FREE} += $perprocesspid{$process_pid}->{MM_PAGE_FREE};
+		$perprocess{$process}->{MM_PAGE_FREE_BATCHED} += $perprocesspid{$process_pid}->{MM_PAGE_FREE_BATCHED};
+		$perprocess{$process}->{MM_PAGE_PCPU_DRAIN} += $perprocesspid{$process_pid}->{MM_PAGE_PCPU_DRAIN};
+		$perprocess{$process}->{HIGH_PCPU_DRAINS} += $perprocesspid{$process_pid}->{HIGH_PCPU_DRAINS};
+		$perprocess{$process}->{HIGH_PCPU_REFILLS} += $perprocesspid{$process_pid}->{HIGH_PCPU_REFILLS};
+		$perprocess{$process}->{MM_PAGE_ALLOC_EXTFRAG} += $perprocesspid{$process_pid}->{MM_PAGE_ALLOC_EXTFRAG};
+		$perprocess{$process}->{HIGH_EXT_FRAG} += $perprocesspid{$process_pid}->{HIGH_EXT_FRAG};
+		$perprocess{$process}->{HIGH_EXT_FRAGMENT_CHANGED} += $perprocesspid{$process_pid}->{HIGH_EXT_FRAGMENT_CHANGED};
+		$perprocess{$process}->{HIGH_EXT_FRAGMENT_SEVERE} += $perprocesspid{$process_pid}->{HIGH_EXT_FRAGMENT_SEVERE};
+		$perprocess{$process}->{HIGH_EXT_FRAGMENT_MODERATE} += $perprocesspid{$process_pid}->{HIGH_EXT_FRAGMENT_MODERATE};
+		$perprocess{$process}->{EVENT_UNKNOWN} += $perprocesspid{$process_pid}->{EVENT_UNKNOWN};
+	}
+}
+
+sub report() {
+	if (!$opt_ignorepid) {
+		dump_stats(\%perprocesspid);
+	} else {
+		aggregate_perprocesspid();
+		dump_stats(\%perprocess);
+	}
+}
+
+# Process events or signals until neither is available
+sub signal_loop() {
+	my $sigint_processed;
+	do {
+		$sigint_processed = 0;
+		process_events();
+
+		# Handle pending signals if any
+		if ($sigint_pending) {
+			my $current_time = time;
+
+			if ($sigint_exit) {
+				print "Received exit signal\n";
+				$sigint_pending = 0;
+			}
+			if ($sigint_report) {
+				if ($current_time >= $sigint_received + 2) {
+					report();
+					$sigint_report = 0;
+					$sigint_pending = 0;
+					$sigint_processed = 1;
+				}
+			}
+		}
+	} while ($sigint_pending || $sigint_processed);
+}
+
+signal_loop();
+report();
diff --git a/Documentation/trace/postprocess/trace-vmscan-postprocess.pl b/Documentation/trace/postprocess/trace-vmscan-postprocess.pl
new file mode 100644
index 000000000..8f961ef2b
--- /dev/null
+++ b/Documentation/trace/postprocess/trace-vmscan-postprocess.pl
@@ -0,0 +1,757 @@
+#!/usr/bin/perl
+# This is a POC for reading the text representation of trace output related to
+# page reclaim. It makes an attempt to extract some high-level information on
+# what is going on. The accuracy of the parser may vary
+#
+# Example usage: trace-vmscan-postprocess.pl < /sys/kernel/debug/tracing/trace_pipe
+# other options
+#   --read-procstat	If the trace lacks process info, get it from /proc
+#   --ignore-pid	Aggregate processes of the same name together
+#
+# Copyright (c) IBM Corporation 2009
+# Author: Mel Gorman <mel@csn.ul.ie>
+use strict;
+use Getopt::Long;
+
+# Tracepoint events
+use constant MM_VMSCAN_DIRECT_RECLAIM_BEGIN	=> 1;
+use constant MM_VMSCAN_DIRECT_RECLAIM_END	=> 2;
+use constant MM_VMSCAN_KSWAPD_WAKE		=> 3;
+use constant MM_VMSCAN_KSWAPD_SLEEP		=> 4;
+use constant MM_VMSCAN_LRU_SHRINK_ACTIVE	=> 5;
+use constant MM_VMSCAN_LRU_SHRINK_INACTIVE	=> 6;
+use constant MM_VMSCAN_LRU_ISOLATE		=> 7;
+use constant MM_VMSCAN_WRITEPAGE_FILE_SYNC	=> 8;
+use constant MM_VMSCAN_WRITEPAGE_ANON_SYNC	=> 9;
+use constant MM_VMSCAN_WRITEPAGE_FILE_ASYNC	=> 10;
+use constant MM_VMSCAN_WRITEPAGE_ANON_ASYNC	=> 11;
+use constant MM_VMSCAN_WRITEPAGE_ASYNC		=> 12;
+use constant EVENT_UNKNOWN			=> 13;
+
+# Per-order events
+use constant MM_VMSCAN_DIRECT_RECLAIM_BEGIN_PERORDER => 11;
+use constant MM_VMSCAN_WAKEUP_KSWAPD_PERORDER 	=> 12;
+use constant MM_VMSCAN_KSWAPD_WAKE_PERORDER	=> 13;
+use constant HIGH_KSWAPD_REWAKEUP_PERORDER	=> 14;
+
+# Constants used to track state
+use constant STATE_DIRECT_BEGIN 		=> 15;
+use constant STATE_DIRECT_ORDER 		=> 16;
+use constant STATE_KSWAPD_BEGIN			=> 17;
+use constant STATE_KSWAPD_ORDER			=> 18;
+
+# High-level events extrapolated from tracepoints
+use constant HIGH_DIRECT_RECLAIM_LATENCY	=> 19;
+use constant HIGH_KSWAPD_LATENCY		=> 20;
+use constant HIGH_KSWAPD_REWAKEUP		=> 21;
+use constant HIGH_NR_SCANNED			=> 22;
+use constant HIGH_NR_TAKEN			=> 23;
+use constant HIGH_NR_RECLAIMED			=> 24;
+use constant HIGH_NR_FILE_SCANNED		=> 25;
+use constant HIGH_NR_ANON_SCANNED		=> 26;
+use constant HIGH_NR_FILE_RECLAIMED		=> 27;
+use constant HIGH_NR_ANON_RECLAIMED		=> 28;
+
+my %perprocesspid;
+my %perprocess;
+my %last_procmap;
+my $opt_ignorepid;
+my $opt_read_procstat;
+
+my $total_wakeup_kswapd;
+my ($total_direct_reclaim, $total_direct_nr_scanned);
+my ($total_direct_nr_file_scanned, $total_direct_nr_anon_scanned);
+my ($total_direct_latency, $total_kswapd_latency);
+my ($total_direct_nr_reclaimed);
+my ($total_direct_nr_file_reclaimed, $total_direct_nr_anon_reclaimed);
+my ($total_direct_writepage_file_sync, $total_direct_writepage_file_async);
+my ($total_direct_writepage_anon_sync, $total_direct_writepage_anon_async);
+my ($total_kswapd_nr_scanned, $total_kswapd_wake);
+my ($total_kswapd_nr_file_scanned, $total_kswapd_nr_anon_scanned);
+my ($total_kswapd_writepage_file_sync, $total_kswapd_writepage_file_async);
+my ($total_kswapd_writepage_anon_sync, $total_kswapd_writepage_anon_async);
+my ($total_kswapd_nr_reclaimed);
+my ($total_kswapd_nr_file_reclaimed, $total_kswapd_nr_anon_reclaimed);
+
+# Catch sigint and exit on request
+my $sigint_report = 0;
+my $sigint_exit = 0;
+my $sigint_pending = 0;
+my $sigint_received = 0;
+sub sigint_handler {
+	my $current_time = time;
+	if ($current_time - 2 > $sigint_received) {
+		print "SIGINT received, report pending. Hit ctrl-c again to exit\n";
+		$sigint_report = 1;
+	} else {
+		if (!$sigint_exit) {
+			print "Second SIGINT received quickly, exiting\n";
+		}
+		$sigint_exit++;
+	}
+
+	if ($sigint_exit > 3) {
+		print "Many SIGINTs received, exiting now without report\n";
+		exit;
+	}
+
+	$sigint_received = $current_time;
+	$sigint_pending = 1;
+}
+$SIG{INT} = "sigint_handler";
+
+# Parse command line options
+GetOptions(
+	'ignore-pid'	 =>	\$opt_ignorepid,
+	'read-procstat'	 =>	\$opt_read_procstat,
+);
+
+# Defaults for dynamically discovered regex's
+my $regex_direct_begin_default = 'order=([0-9]*) may_writepage=([0-9]*) gfp_flags=([A-Z_|]*)';
+my $regex_direct_end_default = 'nr_reclaimed=([0-9]*)';
+my $regex_kswapd_wake_default = 'nid=([0-9]*) order=([0-9]*)';
+my $regex_kswapd_sleep_default = 'nid=([0-9]*)';
+my $regex_wakeup_kswapd_default = 'nid=([0-9]*) zid=([0-9]*) order=([0-9]*)';
+my $regex_lru_isolate_default = 'isolate_mode=([0-9]*) order=([0-9]*) nr_requested=([0-9]*) nr_scanned=([0-9]*) nr_taken=([0-9]*) file=([0-9]*)';
+my $regex_lru_shrink_inactive_default = 'nid=([0-9]*) zid=([0-9]*) nr_scanned=([0-9]*) nr_reclaimed=([0-9]*) priority=([0-9]*) flags=([A-Z_|]*)';
+my $regex_lru_shrink_active_default = 'lru=([A-Z_]*) nr_scanned=([0-9]*) nr_rotated=([0-9]*) priority=([0-9]*)';
+my $regex_writepage_default = 'page=([0-9a-f]*) pfn=([0-9]*) flags=([A-Z_|]*)';
+
+# Dyanically discovered regex
+my $regex_direct_begin;
+my $regex_direct_end;
+my $regex_kswapd_wake;
+my $regex_kswapd_sleep;
+my $regex_wakeup_kswapd;
+my $regex_lru_isolate;
+my $regex_lru_shrink_inactive;
+my $regex_lru_shrink_active;
+my $regex_writepage;
+
+# Static regex used. Specified like this for readability and for use with /o
+#                      (process_pid)     (cpus      )   ( time  )   (tpoint    ) (details)
+my $regex_traceevent = '\s*([a-zA-Z0-9-]*)\s*(\[[0-9]*\])(\s*[dX.][Nnp.][Hhs.][0-9a-fA-F.]*|)\s*([0-9.]*):\s*([a-zA-Z_]*):\s*(.*)';
+my $regex_statname = '[-0-9]*\s\((.*)\).*';
+my $regex_statppid = '[-0-9]*\s\(.*\)\s[A-Za-z]\s([0-9]*).*';
+
+sub generate_traceevent_regex {
+	my $event = shift;
+	my $default = shift;
+	my $regex;
+
+	# Read the event format or use the default
+	if (!open (FORMAT, "/sys/kernel/debug/tracing/events/$event/format")) {
+		print("WARNING: Event $event format string not found\n");
+		return $default;
+	} else {
+		my $line;
+		while (!eof(FORMAT)) {
+			$line = <FORMAT>;
+			$line =~ s/, REC->.*//;
+			if ($line =~ /^print fmt:\s"(.*)".*/) {
+				$regex = $1;
+				$regex =~ s/%s/\([0-9a-zA-Z|_]*\)/g;
+				$regex =~ s/%p/\([0-9a-f]*\)/g;
+				$regex =~ s/%d/\([-0-9]*\)/g;
+				$regex =~ s/%ld/\([-0-9]*\)/g;
+				$regex =~ s/%lu/\([0-9]*\)/g;
+			}
+		}
+	}
+
+	# Can't handle the print_flags stuff but in the context of this
+	# script, it really doesn't matter
+	$regex =~ s/\(REC.*\) \? __print_flags.*//;
+
+	# Verify fields are in the right order
+	my $tuple;
+	foreach $tuple (split /\s/, $regex) {
+		my ($key, $value) = split(/=/, $tuple);
+		my $expected = shift;
+		if ($key ne $expected) {
+			print("WARNING: Format not as expected for event $event '$key' != '$expected'\n");
+			$regex =~ s/$key=\((.*)\)/$key=$1/;
+		}
+	}
+
+	if (defined shift) {
+		die("Fewer fields than expected in format");
+	}
+
+	return $regex;
+}
+
+$regex_direct_begin = generate_traceevent_regex(
+			"vmscan/mm_vmscan_direct_reclaim_begin",
+			$regex_direct_begin_default,
+			"order", "may_writepage",
+			"gfp_flags");
+$regex_direct_end = generate_traceevent_regex(
+			"vmscan/mm_vmscan_direct_reclaim_end",
+			$regex_direct_end_default,
+			"nr_reclaimed");
+$regex_kswapd_wake = generate_traceevent_regex(
+			"vmscan/mm_vmscan_kswapd_wake",
+			$regex_kswapd_wake_default,
+			"nid", "order");
+$regex_kswapd_sleep = generate_traceevent_regex(
+			"vmscan/mm_vmscan_kswapd_sleep",
+			$regex_kswapd_sleep_default,
+			"nid");
+$regex_wakeup_kswapd = generate_traceevent_regex(
+			"vmscan/mm_vmscan_wakeup_kswapd",
+			$regex_wakeup_kswapd_default,
+			"nid", "zid", "order");
+$regex_lru_isolate = generate_traceevent_regex(
+			"vmscan/mm_vmscan_lru_isolate",
+			$regex_lru_isolate_default,
+			"isolate_mode", "order",
+			"nr_requested", "nr_scanned", "nr_taken",
+			"file");
+$regex_lru_shrink_inactive = generate_traceevent_regex(
+			"vmscan/mm_vmscan_lru_shrink_inactive",
+			$regex_lru_shrink_inactive_default,
+			"nid", "zid",
+			"nr_scanned", "nr_reclaimed", "priority",
+			"flags");
+$regex_lru_shrink_active = generate_traceevent_regex(
+			"vmscan/mm_vmscan_lru_shrink_active",
+			$regex_lru_shrink_active_default,
+			"nid", "zid",
+			"lru",
+			"nr_scanned", "nr_rotated", "priority");
+$regex_writepage = generate_traceevent_regex(
+			"vmscan/mm_vmscan_writepage",
+			$regex_writepage_default,
+			"page", "pfn", "flags");
+
+sub read_statline($) {
+	my $pid = $_[0];
+	my $statline;
+
+	if (open(STAT, "/proc/$pid/stat")) {
+		$statline = <STAT>;
+		close(STAT);
+	}
+
+	if ($statline eq '') {
+		$statline = "-1 (UNKNOWN_PROCESS_NAME) R 0";
+	}
+
+	return $statline;
+}
+
+sub guess_process_pid($$) {
+	my $pid = $_[0];
+	my $statline = $_[1];
+
+	if ($pid == 0) {
+		return "swapper-0";
+	}
+
+	if ($statline !~ /$regex_statname/o) {
+		die("Failed to math stat line for process name :: $statline");
+	}
+	return "$1-$pid";
+}
+
+# Convert sec.usec timestamp format
+sub timestamp_to_ms($) {
+	my $timestamp = $_[0];
+
+	my ($sec, $usec) = split (/\./, $timestamp);
+	return ($sec * 1000) + ($usec / 1000);
+}
+
+sub process_events {
+	my $traceevent;
+	my $process_pid;
+	my $cpus;
+	my $timestamp;
+	my $tracepoint;
+	my $details;
+	my $statline;
+
+	# Read each line of the event log
+EVENT_PROCESS:
+	while ($traceevent = <STDIN>) {
+		if ($traceevent =~ /$regex_traceevent/o) {
+			$process_pid = $1;
+			$timestamp = $4;
+			$tracepoint = $5;
+
+			$process_pid =~ /(.*)-([0-9]*)$/;
+			my $process = $1;
+			my $pid = $2;
+
+			if ($process eq "") {
+				$process = $last_procmap{$pid};
+				$process_pid = "$process-$pid";
+			}
+			$last_procmap{$pid} = $process;
+
+			if ($opt_read_procstat) {
+				$statline = read_statline($pid);
+				if ($opt_read_procstat && $process eq '') {
+					$process_pid = guess_process_pid($pid, $statline);
+				}
+			}
+		} else {
+			next;
+		}
+
+		# Perl Switch() sucks majorly
+		if ($tracepoint eq "mm_vmscan_direct_reclaim_begin") {
+			$timestamp = timestamp_to_ms($timestamp);
+			$perprocesspid{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN}++;
+			$perprocesspid{$process_pid}->{STATE_DIRECT_BEGIN} = $timestamp;
+
+			$details = $6;
+			if ($details !~ /$regex_direct_begin/o) {
+				print "WARNING: Failed to parse mm_vmscan_direct_reclaim_begin as expected\n";
+				print "         $details\n";
+				print "         $regex_direct_begin\n";
+				next;
+			}
+			my $order = $1;
+			$perprocesspid{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN_PERORDER}[$order]++;
+			$perprocesspid{$process_pid}->{STATE_DIRECT_ORDER} = $order;
+		} elsif ($tracepoint eq "mm_vmscan_direct_reclaim_end") {
+			# Count the event itself
+			my $index = $perprocesspid{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_END};
+			$perprocesspid{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_END}++;
+
+			# Record how long direct reclaim took this time
+			if (defined $perprocesspid{$process_pid}->{STATE_DIRECT_BEGIN}) {
+				$timestamp = timestamp_to_ms($timestamp);
+				my $order = $perprocesspid{$process_pid}->{STATE_DIRECT_ORDER};
+				my $latency = ($timestamp - $perprocesspid{$process_pid}->{STATE_DIRECT_BEGIN});
+				$perprocesspid{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index] = "$order-$latency";
+			}
+		} elsif ($tracepoint eq "mm_vmscan_kswapd_wake") {
+			$details = $6;
+			if ($details !~ /$regex_kswapd_wake/o) {
+				print "WARNING: Failed to parse mm_vmscan_kswapd_wake as expected\n";
+				print "         $details\n";
+				print "         $regex_kswapd_wake\n";
+				next;
+			}
+
+			my $order = $2;
+			$perprocesspid{$process_pid}->{STATE_KSWAPD_ORDER} = $order;
+			if (!$perprocesspid{$process_pid}->{STATE_KSWAPD_BEGIN}) {
+				$timestamp = timestamp_to_ms($timestamp);
+				$perprocesspid{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE}++;
+				$perprocesspid{$process_pid}->{STATE_KSWAPD_BEGIN} = $timestamp;
+				$perprocesspid{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE_PERORDER}[$order]++;
+			} else {
+				$perprocesspid{$process_pid}->{HIGH_KSWAPD_REWAKEUP}++;
+				$perprocesspid{$process_pid}->{HIGH_KSWAPD_REWAKEUP_PERORDER}[$order]++;
+			}
+		} elsif ($tracepoint eq "mm_vmscan_kswapd_sleep") {
+
+			# Count the event itself
+			my $index = $perprocesspid{$process_pid}->{MM_VMSCAN_KSWAPD_SLEEP};
+			$perprocesspid{$process_pid}->{MM_VMSCAN_KSWAPD_SLEEP}++;
+
+			# Record how long kswapd was awake
+			$timestamp = timestamp_to_ms($timestamp);
+			my $order = $perprocesspid{$process_pid}->{STATE_KSWAPD_ORDER};
+			my $latency = ($timestamp - $perprocesspid{$process_pid}->{STATE_KSWAPD_BEGIN});
+			$perprocesspid{$process_pid}->{HIGH_KSWAPD_LATENCY}[$index] = "$order-$latency";
+			$perprocesspid{$process_pid}->{STATE_KSWAPD_BEGIN} = 0;
+		} elsif ($tracepoint eq "mm_vmscan_wakeup_kswapd") {
+			$perprocesspid{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD}++;
+
+			$details = $6;
+			if ($details !~ /$regex_wakeup_kswapd/o) {
+				print "WARNING: Failed to parse mm_vmscan_wakeup_kswapd as expected\n";
+				print "         $details\n";
+				print "         $regex_wakeup_kswapd\n";
+				next;
+			}
+			my $order = $3;
+			$perprocesspid{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD_PERORDER}[$order]++;
+		} elsif ($tracepoint eq "mm_vmscan_lru_isolate") {
+			$details = $6;
+			if ($details !~ /$regex_lru_isolate/o) {
+				print "WARNING: Failed to parse mm_vmscan_lru_isolate as expected\n";
+				print "         $details\n";
+				print "         $regex_lru_isolate/o\n";
+				next;
+			}
+			my $isolate_mode = $1;
+			my $nr_scanned = $4;
+			my $file = $6;
+
+			# To closer match vmstat scanning statistics, only count isolate_both
+			# and isolate_inactive as scanning. isolate_active is rotation
+			# isolate_inactive == 1
+			# isolate_active   == 2
+			# isolate_both     == 3
+			if ($isolate_mode != 2) {
+				$perprocesspid{$process_pid}->{HIGH_NR_SCANNED} += $nr_scanned;
+				if ($file == 1) {
+					$perprocesspid{$process_pid}->{HIGH_NR_FILE_SCANNED} += $nr_scanned;
+				} else {
+					$perprocesspid{$process_pid}->{HIGH_NR_ANON_SCANNED} += $nr_scanned;
+				}
+			}
+		} elsif ($tracepoint eq "mm_vmscan_lru_shrink_inactive") {
+			$details = $6;
+			if ($details !~ /$regex_lru_shrink_inactive/o) {
+				print "WARNING: Failed to parse mm_vmscan_lru_shrink_inactive as expected\n";
+				print "         $details\n";
+				print "         $regex_lru_shrink_inactive/o\n";
+				next;
+			}
+
+			my $nr_reclaimed = $4;
+			my $flags = $6;
+			my $file = 0;
+			if ($flags =~ /RECLAIM_WB_FILE/) {
+				$file = 1;
+			}
+			$perprocesspid{$process_pid}->{HIGH_NR_RECLAIMED} += $nr_reclaimed;
+			if ($file) {
+				$perprocesspid{$process_pid}->{HIGH_NR_FILE_RECLAIMED} += $nr_reclaimed;
+			} else {
+				$perprocesspid{$process_pid}->{HIGH_NR_ANON_RECLAIMED} += $nr_reclaimed;
+			}
+		} elsif ($tracepoint eq "mm_vmscan_writepage") {
+			$details = $6;
+			if ($details !~ /$regex_writepage/o) {
+				print "WARNING: Failed to parse mm_vmscan_writepage as expected\n";
+				print "         $details\n";
+				print "         $regex_writepage\n";
+				next;
+			}
+
+			my $flags = $3;
+			my $file = 0;
+			my $sync_io = 0;
+			if ($flags =~ /RECLAIM_WB_FILE/) {
+				$file = 1;
+			}
+			if ($flags =~ /RECLAIM_WB_SYNC/) {
+				$sync_io = 1;
+			}
+			if ($sync_io) {
+				if ($file) {
+					$perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC}++;
+				} else {
+					$perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC}++;
+				}
+			} else {
+				if ($file) {
+					$perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC}++;
+				} else {
+					$perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC}++;
+				}
+			}
+		} else {
+			$perprocesspid{$process_pid}->{EVENT_UNKNOWN}++;
+		}
+
+		if ($sigint_pending) {
+			last EVENT_PROCESS;
+		}
+	}
+}
+
+sub dump_stats {
+	my $hashref = shift;
+	my %stats = %$hashref;
+
+	# Dump per-process stats
+	my $process_pid;
+	my $max_strlen = 0;
+
+	# Get the maximum process name
+	foreach $process_pid (keys %perprocesspid) {
+		my $len = length($process_pid);
+		if ($len > $max_strlen) {
+			$max_strlen = $len;
+		}
+	}
+	$max_strlen += 2;
+
+	# Work out latencies
+	printf("\n") if !$opt_ignorepid;
+	printf("Reclaim latencies expressed as order-latency_in_ms\n") if !$opt_ignorepid;
+	foreach $process_pid (keys %stats) {
+
+		if (!$stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[0] &&
+				!$stats{$process_pid}->{HIGH_KSWAPD_LATENCY}[0]) {
+			next;
+		}
+
+		printf "%-" . $max_strlen . "s ", $process_pid if !$opt_ignorepid;
+		my $index = 0;
+		while (defined $stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index] ||
+			defined $stats{$process_pid}->{HIGH_KSWAPD_LATENCY}[$index]) {
+
+			if ($stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index]) {
+				printf("%s ", $stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index]) if !$opt_ignorepid;
+				my ($dummy, $latency) = split(/-/, $stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index]);
+				$total_direct_latency += $latency;
+			} else {
+				printf("%s ", $stats{$process_pid}->{HIGH_KSWAPD_LATENCY}[$index]) if !$opt_ignorepid;
+				my ($dummy, $latency) = split(/-/, $stats{$process_pid}->{HIGH_KSWAPD_LATENCY}[$index]);
+				$total_kswapd_latency += $latency;
+			}
+			$index++;
+		}
+		print "\n" if !$opt_ignorepid;
+	}
+
+	# Print out process activity
+	printf("\n");
+	printf("%-" . $max_strlen . "s %8s %10s   %8s %8s  %8s %8s %8s %8s\n", "Process", "Direct",  "Wokeup", "Pages",   "Pages",   "Pages",   "Pages",     "Time");
+	printf("%-" . $max_strlen . "s %8s %10s   %8s %8s  %8s %8s %8s %8s\n", "details", "Rclms",   "Kswapd", "Scanned", "Rclmed",  "Sync-IO", "ASync-IO",  "Stalled");
+	foreach $process_pid (keys %stats) {
+
+		if (!$stats{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN}) {
+			next;
+		}
+
+		$total_direct_reclaim += $stats{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN};
+		$total_wakeup_kswapd += $stats{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD};
+		$total_direct_nr_scanned += $stats{$process_pid}->{HIGH_NR_SCANNED};
+		$total_direct_nr_file_scanned += $stats{$process_pid}->{HIGH_NR_FILE_SCANNED};
+		$total_direct_nr_anon_scanned += $stats{$process_pid}->{HIGH_NR_ANON_SCANNED};
+		$total_direct_nr_reclaimed += $stats{$process_pid}->{HIGH_NR_RECLAIMED};
+		$total_direct_nr_file_reclaimed += $stats{$process_pid}->{HIGH_NR_FILE_RECLAIMED};
+		$total_direct_nr_anon_reclaimed += $stats{$process_pid}->{HIGH_NR_ANON_RECLAIMED};
+		$total_direct_writepage_file_sync += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC};
+		$total_direct_writepage_anon_sync += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC};
+		$total_direct_writepage_file_async += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC};
+
+		$total_direct_writepage_anon_async += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC};
+
+		my $index = 0;
+		my $this_reclaim_delay = 0;
+		while (defined $stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index]) {
+			 my ($dummy, $latency) = split(/-/, $stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index]);
+			$this_reclaim_delay += $latency;
+			$index++;
+		}
+
+		printf("%-" . $max_strlen . "s %8d %10d   %8u %8u  %8u %8u %8.3f",
+			$process_pid,
+			$stats{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN},
+			$stats{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD},
+			$stats{$process_pid}->{HIGH_NR_SCANNED},
+			$stats{$process_pid}->{HIGH_NR_FILE_SCANNED},
+			$stats{$process_pid}->{HIGH_NR_ANON_SCANNED},
+			$stats{$process_pid}->{HIGH_NR_RECLAIMED},
+			$stats{$process_pid}->{HIGH_NR_FILE_RECLAIMED},
+			$stats{$process_pid}->{HIGH_NR_ANON_RECLAIMED},
+			$stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC} + $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC},
+			$stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC} + $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC},
+			$this_reclaim_delay / 1000);
+
+		if ($stats{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN}) {
+			print "      ";
+			for (my $order = 0; $order < 20; $order++) {
+				my $count = $stats{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN_PERORDER}[$order];
+				if ($count != 0) {
+					print "direct-$order=$count ";
+				}
+			}
+		}
+		if ($stats{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD}) {
+			print "      ";
+			for (my $order = 0; $order < 20; $order++) {
+				my $count = $stats{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD_PERORDER}[$order];
+				if ($count != 0) {
+					print "wakeup-$order=$count ";
+				}
+			}
+		}
+
+		print "\n";
+	}
+
+	# Print out kswapd activity
+	printf("\n");
+	printf("%-" . $max_strlen . "s %8s %10s   %8s   %8s %8s %8s\n", "Kswapd",   "Kswapd",  "Order",     "Pages",   "Pages",   "Pages",  "Pages");
+	printf("%-" . $max_strlen . "s %8s %10s   %8s   %8s %8s %8s\n", "Instance", "Wakeups", "Re-wakeup", "Scanned", "Rclmed",  "Sync-IO", "ASync-IO");
+	foreach $process_pid (keys %stats) {
+
+		if (!$stats{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE}) {
+			next;
+		}
+
+		$total_kswapd_wake += $stats{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE};
+		$total_kswapd_nr_scanned += $stats{$process_pid}->{HIGH_NR_SCANNED};
+		$total_kswapd_nr_file_scanned += $stats{$process_pid}->{HIGH_NR_FILE_SCANNED};
+		$total_kswapd_nr_anon_scanned += $stats{$process_pid}->{HIGH_NR_ANON_SCANNED};
+		$total_kswapd_nr_reclaimed += $stats{$process_pid}->{HIGH_NR_RECLAIMED};
+		$total_kswapd_nr_file_reclaimed += $stats{$process_pid}->{HIGH_NR_FILE_RECLAIMED};
+		$total_kswapd_nr_anon_reclaimed += $stats{$process_pid}->{HIGH_NR_ANON_RECLAIMED};
+		$total_kswapd_writepage_file_sync += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC};
+		$total_kswapd_writepage_anon_sync += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC};
+		$total_kswapd_writepage_file_async += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC};
+		$total_kswapd_writepage_anon_async += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC};
+
+		printf("%-" . $max_strlen . "s %8d %10d   %8u %8u  %8i %8u",
+			$process_pid,
+			$stats{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE},
+			$stats{$process_pid}->{HIGH_KSWAPD_REWAKEUP},
+			$stats{$process_pid}->{HIGH_NR_SCANNED},
+			$stats{$process_pid}->{HIGH_NR_FILE_SCANNED},
+			$stats{$process_pid}->{HIGH_NR_ANON_SCANNED},
+			$stats{$process_pid}->{HIGH_NR_RECLAIMED},
+			$stats{$process_pid}->{HIGH_NR_FILE_RECLAIMED},
+			$stats{$process_pid}->{HIGH_NR_ANON_RECLAIMED},
+			$stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC} + $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC},
+			$stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC} + $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC});
+
+		if ($stats{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE}) {
+			print "      ";
+			for (my $order = 0; $order < 20; $order++) {
+				my $count = $stats{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE_PERORDER}[$order];
+				if ($count != 0) {
+					print "wake-$order=$count ";
+				}
+			}
+		}
+		if ($stats{$process_pid}->{HIGH_KSWAPD_REWAKEUP}) {
+			print "      ";
+			for (my $order = 0; $order < 20; $order++) {
+				my $count = $stats{$process_pid}->{HIGH_KSWAPD_REWAKEUP_PERORDER}[$order];
+				if ($count != 0) {
+					print "rewake-$order=$count ";
+				}
+			}
+		}
+		printf("\n");
+	}
+
+	# Print out summaries
+	$total_direct_latency /= 1000;
+	$total_kswapd_latency /= 1000;
+	print "\nSummary\n";
+	print "Direct reclaims:     			$total_direct_reclaim\n";
+	print "Direct reclaim pages scanned:		$total_direct_nr_scanned\n";
+	print "Direct reclaim file pages scanned:	$total_direct_nr_file_scanned\n";
+	print "Direct reclaim anon pages scanned:	$total_direct_nr_anon_scanned\n";
+	print "Direct reclaim pages reclaimed:		$total_direct_nr_reclaimed\n";
+	print "Direct reclaim file pages reclaimed:	$total_direct_nr_file_reclaimed\n";
+	print "Direct reclaim anon pages reclaimed:	$total_direct_nr_anon_reclaimed\n";
+	print "Direct reclaim write file sync I/O:	$total_direct_writepage_file_sync\n";
+	print "Direct reclaim write anon sync I/O:	$total_direct_writepage_anon_sync\n";
+	print "Direct reclaim write file async I/O:	$total_direct_writepage_file_async\n";
+	print "Direct reclaim write anon async I/O:	$total_direct_writepage_anon_async\n";
+	print "Wake kswapd requests:			$total_wakeup_kswapd\n";
+	printf "Time stalled direct reclaim: 		%-1.2f seconds\n", $total_direct_latency;
+	print "\n";
+	print "Kswapd wakeups:				$total_kswapd_wake\n";
+	print "Kswapd pages scanned:			$total_kswapd_nr_scanned\n";
+	print "Kswapd file pages scanned:		$total_kswapd_nr_file_scanned\n";
+	print "Kswapd anon pages scanned:		$total_kswapd_nr_anon_scanned\n";
+	print "Kswapd pages reclaimed:			$total_kswapd_nr_reclaimed\n";
+	print "Kswapd file pages reclaimed:		$total_kswapd_nr_file_reclaimed\n";
+	print "Kswapd anon pages reclaimed:		$total_kswapd_nr_anon_reclaimed\n";
+	print "Kswapd reclaim write file sync I/O:	$total_kswapd_writepage_file_sync\n";
+	print "Kswapd reclaim write anon sync I/O:	$total_kswapd_writepage_anon_sync\n";
+	print "Kswapd reclaim write file async I/O:	$total_kswapd_writepage_file_async\n";
+	print "Kswapd reclaim write anon async I/O:	$total_kswapd_writepage_anon_async\n";
+	printf "Time kswapd awake:			%-1.2f seconds\n", $total_kswapd_latency;
+}
+
+sub aggregate_perprocesspid() {
+	my $process_pid;
+	my $process;
+	undef %perprocess;
+
+	foreach $process_pid (keys %perprocesspid) {
+		$process = $process_pid;
+		$process =~ s/-([0-9])*$//;
+		if ($process eq '') {
+			$process = "NO_PROCESS_NAME";
+		}
+
+		$perprocess{$process}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN} += $perprocesspid{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN};
+		$perprocess{$process}->{MM_VMSCAN_KSWAPD_WAKE} += $perprocesspid{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE};
+		$perprocess{$process}->{MM_VMSCAN_WAKEUP_KSWAPD} += $perprocesspid{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD};
+		$perprocess{$process}->{HIGH_KSWAPD_REWAKEUP} += $perprocesspid{$process_pid}->{HIGH_KSWAPD_REWAKEUP};
+		$perprocess{$process}->{HIGH_NR_SCANNED} += $perprocesspid{$process_pid}->{HIGH_NR_SCANNED};
+		$perprocess{$process}->{HIGH_NR_FILE_SCANNED} += $perprocesspid{$process_pid}->{HIGH_NR_FILE_SCANNED};
+		$perprocess{$process}->{HIGH_NR_ANON_SCANNED} += $perprocesspid{$process_pid}->{HIGH_NR_ANON_SCANNED};
+		$perprocess{$process}->{HIGH_NR_RECLAIMED} += $perprocesspid{$process_pid}->{HIGH_NR_RECLAIMED};
+		$perprocess{$process}->{HIGH_NR_FILE_RECLAIMED} += $perprocesspid{$process_pid}->{HIGH_NR_FILE_RECLAIMED};
+		$perprocess{$process}->{HIGH_NR_ANON_RECLAIMED} += $perprocesspid{$process_pid}->{HIGH_NR_ANON_RECLAIMED};
+		$perprocess{$process}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC} += $perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC};
+		$perprocess{$process}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC} += $perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC};
+		$perprocess{$process}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC} += $perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC};
+		$perprocess{$process}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC} += $perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC};
+
+		for (my $order = 0; $order < 20; $order++) {
+			$perprocess{$process}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN_PERORDER}[$order] += $perprocesspid{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN_PERORDER}[$order];
+			$perprocess{$process}->{MM_VMSCAN_WAKEUP_KSWAPD_PERORDER}[$order] += $perprocesspid{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD_PERORDER}[$order];
+			$perprocess{$process}->{MM_VMSCAN_KSWAPD_WAKE_PERORDER}[$order] += $perprocesspid{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE_PERORDER}[$order];
+
+		}
+
+		# Aggregate direct reclaim latencies
+		my $wr_index = $perprocess{$process}->{MM_VMSCAN_DIRECT_RECLAIM_END};
+		my $rd_index = 0;
+		while (defined $perprocesspid{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$rd_index]) {
+			$perprocess{$process}->{HIGH_DIRECT_RECLAIM_LATENCY}[$wr_index] = $perprocesspid{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$rd_index];
+			$rd_index++;
+			$wr_index++;
+		}
+		$perprocess{$process}->{MM_VMSCAN_DIRECT_RECLAIM_END} = $wr_index;
+
+		# Aggregate kswapd latencies
+		my $wr_index = $perprocess{$process}->{MM_VMSCAN_KSWAPD_SLEEP};
+		my $rd_index = 0;
+		while (defined $perprocesspid{$process_pid}->{HIGH_KSWAPD_LATENCY}[$rd_index]) {
+			$perprocess{$process}->{HIGH_KSWAPD_LATENCY}[$wr_index] = $perprocesspid{$process_pid}->{HIGH_KSWAPD_LATENCY}[$rd_index];
+			$rd_index++;
+			$wr_index++;
+		}
+		$perprocess{$process}->{MM_VMSCAN_DIRECT_RECLAIM_END} = $wr_index;
+	}
+}
+
+sub report() {
+	if (!$opt_ignorepid) {
+		dump_stats(\%perprocesspid);
+	} else {
+		aggregate_perprocesspid();
+		dump_stats(\%perprocess);
+	}
+}
+
+# Process events or signals until neither is available
+sub signal_loop() {
+	my $sigint_processed;
+	do {
+		$sigint_processed = 0;
+		process_events();
+
+		# Handle pending signals if any
+		if ($sigint_pending) {
+			my $current_time = time;
+
+			if ($sigint_exit) {
+				print "Received exit signal\n";
+				$sigint_pending = 0;
+			}
+			if ($sigint_report) {
+				if ($current_time >= $sigint_received + 2) {
+					report();
+					$sigint_report = 0;
+					$sigint_pending = 0;
+					$sigint_processed = 1;
+				}
+			}
+		}
+	} while ($sigint_pending || $sigint_processed);
+}
+
+signal_loop();
+report();
diff --git a/Documentation/trace/ring-buffer-design.txt b/Documentation/trace/ring-buffer-design.txt
new file mode 100644
index 000000000..ff747b6fa
--- /dev/null
+++ b/Documentation/trace/ring-buffer-design.txt
@@ -0,0 +1,955 @@
+		Lockless Ring Buffer Design
+		===========================
+
+Copyright 2009 Red Hat Inc.
+   Author:   Steven Rostedt <srostedt@redhat.com>
+  License:   The GNU Free Documentation License, Version 1.2
+               (dual licensed under the GPL v2)
+Reviewers:   Mathieu Desnoyers, Huang Ying, Hidetoshi Seto,
+	     and Frederic Weisbecker.
+
+
+Written for: 2.6.31
+
+Terminology used in this Document
+---------------------------------
+
+tail - where new writes happen in the ring buffer.
+
+head - where new reads happen in the ring buffer.
+
+producer - the task that writes into the ring buffer (same as writer)
+
+writer - same as producer
+
+consumer - the task that reads from the buffer (same as reader)
+
+reader - same as consumer.
+
+reader_page - A page outside the ring buffer used solely (for the most part)
+    by the reader.
+
+head_page - a pointer to the page that the reader will use next
+
+tail_page - a pointer to the page that will be written to next
+
+commit_page - a pointer to the page with the last finished non-nested write.
+
+cmpxchg - hardware-assisted atomic transaction that performs the following:
+
+   A = B iff previous A == C
+
+   R = cmpxchg(A, C, B) is saying that we replace A with B if and only if
+      current A is equal to C, and we put the old (current) A into R
+
+   R gets the previous A regardless if A is updated with B or not.
+
+   To see if the update was successful a compare of R == C may be used.
+
+The Generic Ring Buffer
+-----------------------
+
+The ring buffer can be used in either an overwrite mode or in
+producer/consumer mode.
+
+Producer/consumer mode is where if the producer were to fill up the
+buffer before the consumer could free up anything, the producer
+will stop writing to the buffer. This will lose most recent events.
+
+Overwrite mode is where if the producer were to fill up the buffer
+before the consumer could free up anything, the producer will
+overwrite the older data. This will lose the oldest events.
+
+No two writers can write at the same time (on the same per-cpu buffer),
+but a writer may interrupt another writer, but it must finish writing
+before the previous writer may continue. This is very important to the
+algorithm. The writers act like a "stack". The way interrupts works
+enforces this behavior.
+
+
+  writer1 start
+     <preempted> writer2 start
+         <preempted> writer3 start
+                     writer3 finishes
+                 writer2 finishes
+  writer1 finishes
+
+This is very much like a writer being preempted by an interrupt and
+the interrupt doing a write as well.
+
+Readers can happen at any time. But no two readers may run at the
+same time, nor can a reader preempt/interrupt another reader. A reader
+cannot preempt/interrupt a writer, but it may read/consume from the
+buffer at the same time as a writer is writing, but the reader must be
+on another processor to do so. A reader may read on its own processor
+and can be preempted by a writer.
+
+A writer can preempt a reader, but a reader cannot preempt a writer.
+But a reader can read the buffer at the same time (on another processor)
+as a writer.
+
+The ring buffer is made up of a list of pages held together by a linked list.
+
+At initialization a reader page is allocated for the reader that is not
+part of the ring buffer.
+
+The head_page, tail_page and commit_page are all initialized to point
+to the same page.
+
+The reader page is initialized to have its next pointer pointing to
+the head page, and its previous pointer pointing to a page before
+the head page.
+
+The reader has its own page to use. At start up time, this page is
+allocated but is not attached to the list. When the reader wants
+to read from the buffer, if its page is empty (like it is on start-up),
+it will swap its page with the head_page. The old reader page will
+become part of the ring buffer and the head_page will be removed.
+The page after the inserted page (old reader_page) will become the
+new head page.
+
+Once the new page is given to the reader, the reader could do what
+it wants with it, as long as a writer has left that page.
+
+A sample of how the reader page is swapped: Note this does not
+show the head page in the buffer, it is for demonstrating a swap
+only.
+
+  +------+
+  |reader|          RING BUFFER
+  |page  |
+  +------+
+                  +---+   +---+   +---+
+                  |   |-->|   |-->|   |
+                  |   |<--|   |<--|   |
+                  +---+   +---+   +---+
+                   ^ |             ^ |
+                   | +-------------+ |
+                   +-----------------+
+
+
+  +------+
+  |reader|          RING BUFFER
+  |page  |-------------------+
+  +------+                   v
+    |             +---+   +---+   +---+
+    |             |   |-->|   |-->|   |
+    |             |   |<--|   |<--|   |<-+
+    |             +---+   +---+   +---+  |
+    |              ^ |             ^ |   |
+    |              | +-------------+ |   |
+    |              +-----------------+   |
+    +------------------------------------+
+
+  +------+
+  |reader|          RING BUFFER
+  |page  |-------------------+
+  +------+ <---------------+ v
+    |  ^          +---+   +---+   +---+
+    |  |          |   |-->|   |-->|   |
+    |  |          |   |   |   |<--|   |<-+
+    |  |          +---+   +---+   +---+  |
+    |  |             |             ^ |   |
+    |  |             +-------------+ |   |
+    |  +-----------------------------+   |
+    +------------------------------------+
+
+  +------+
+  |buffer|          RING BUFFER
+  |page  |-------------------+
+  +------+ <---------------+ v
+    |  ^          +---+   +---+   +---+
+    |  |          |   |   |   |-->|   |
+    |  |  New     |   |   |   |<--|   |<-+
+    |  | Reader   +---+   +---+   +---+  |
+    |  |  page ----^                 |   |
+    |  |                             |   |
+    |  +-----------------------------+   |
+    +------------------------------------+
+
+
+
+It is possible that the page swapped is the commit page and the tail page,
+if what is in the ring buffer is less than what is held in a buffer page.
+
+
+          reader page    commit page   tail page
+              |              |             |
+              v              |             |
+             +---+           |             |
+             |   |<----------+             |
+             |   |<------------------------+
+             |   |------+
+             +---+      |
+                        |
+                        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |--->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+This case is still valid for this algorithm.
+When the writer leaves the page, it simply goes into the ring buffer
+since the reader page still points to the next location in the ring
+buffer.
+
+
+The main pointers:
+
+  reader page - The page used solely by the reader and is not part
+                of the ring buffer (may be swapped in)
+
+  head page - the next page in the ring buffer that will be swapped
+              with the reader page.
+
+  tail page - the page where the next write will take place.
+
+  commit page - the page that last finished a write.
+
+The commit page only is updated by the outermost writer in the
+writer stack. A writer that preempts another writer will not move the
+commit page.
+
+When data is written into the ring buffer, a position is reserved
+in the ring buffer and passed back to the writer. When the writer
+is finished writing data into that position, it commits the write.
+
+Another write (or a read) may take place at anytime during this
+transaction. If another write happens it must finish before continuing
+with the previous write.
+
+
+   Write reserve:
+
+       Buffer page
+      +---------+
+      |written  |
+      +---------+  <--- given back to writer (current commit)
+      |reserved |
+      +---------+ <--- tail pointer
+      | empty   |
+      +---------+
+
+   Write commit:
+
+       Buffer page
+      +---------+
+      |written  |
+      +---------+
+      |written  |
+      +---------+  <--- next position for write (current commit)
+      | empty   |
+      +---------+
+
+
+ If a write happens after the first reserve:
+
+       Buffer page
+      +---------+
+      |written  |
+      +---------+  <-- current commit
+      |reserved |
+      +---------+  <--- given back to second writer
+      |reserved |
+      +---------+ <--- tail pointer
+
+  After second writer commits:
+
+
+       Buffer page
+      +---------+
+      |written  |
+      +---------+  <--(last full commit)
+      |reserved |
+      +---------+
+      |pending  |
+      |commit   |
+      +---------+ <--- tail pointer
+
+  When the first writer commits:
+
+       Buffer page
+      +---------+
+      |written  |
+      +---------+
+      |written  |
+      +---------+
+      |written  |
+      +---------+  <--(last full commit and tail pointer)
+
+
+The commit pointer points to the last write location that was
+committed without preempting another write. When a write that
+preempted another write is committed, it only becomes a pending commit
+and will not be a full commit until all writes have been committed.
+
+The commit page points to the page that has the last full commit.
+The tail page points to the page with the last write (before
+committing).
+
+The tail page is always equal to or after the commit page. It may
+be several pages ahead. If the tail page catches up to the commit
+page then no more writes may take place (regardless of the mode
+of the ring buffer: overwrite and produce/consumer).
+
+The order of pages is:
+
+ head page
+ commit page
+ tail page
+
+Possible scenario:
+                             tail page
+  head page         commit page  |
+      |                 |        |
+      v                 v        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |--->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+There is a special case that the head page is after either the commit page
+and possibly the tail page. That is when the commit (and tail) page has been
+swapped with the reader page. This is because the head page is always
+part of the ring buffer, but the reader page is not. Whenever there
+has been less than a full page that has been committed inside the ring buffer,
+and a reader swaps out a page, it will be swapping out the commit page.
+
+
+          reader page    commit page   tail page
+              |              |             |
+              v              |             |
+             +---+           |             |
+             |   |<----------+             |
+             |   |<------------------------+
+             |   |------+
+             +---+      |
+                        |
+                        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |--->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+                        ^
+                        |
+                    head page
+
+
+In this case, the head page will not move when the tail and commit
+move back into the ring buffer.
+
+The reader cannot swap a page into the ring buffer if the commit page
+is still on that page. If the read meets the last commit (real commit
+not pending or reserved), then there is nothing more to read.
+The buffer is considered empty until another full commit finishes.
+
+When the tail meets the head page, if the buffer is in overwrite mode,
+the head page will be pushed ahead one. If the buffer is in producer/consumer
+mode, the write will fail.
+
+Overwrite mode:
+
+            tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |--->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+                        ^
+                        |
+                    head page
+
+
+            tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |--->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+                                 ^
+                                 |
+                             head page
+
+
+                    tail page
+                        |
+                        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |--->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+                                 ^
+                                 |
+                             head page
+
+Note, the reader page will still point to the previous head page.
+But when a swap takes place, it will use the most recent head page.
+
+
+Making the Ring Buffer Lockless:
+--------------------------------
+
+The main idea behind the lockless algorithm is to combine the moving
+of the head_page pointer with the swapping of pages with the reader.
+State flags are placed inside the pointer to the page. To do this,
+each page must be aligned in memory by 4 bytes. This will allow the 2
+least significant bits of the address to be used as flags, since
+they will always be zero for the address. To get the address,
+simply mask out the flags.
+
+  MASK = ~3
+
+  address & MASK
+
+Two flags will be kept by these two bits:
+
+   HEADER - the page being pointed to is a head page
+
+   UPDATE - the page being pointed to is being updated by a writer
+          and was or is about to be a head page.
+
+
+          reader page
+              |
+              v
+             +---+
+             |   |------+
+             +---+      |
+                        |
+                        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-H->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+
+The above pointer "-H->" would have the HEADER flag set. That is
+the next page is the next page to be swapped out by the reader.
+This pointer means the next page is the head page.
+
+When the tail page meets the head pointer, it will use cmpxchg to
+change the pointer to the UPDATE state:
+
+
+            tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-H->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+            tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+"-U->" represents a pointer in the UPDATE state.
+
+Any access to the reader will need to take some sort of lock to serialize
+the readers. But the writers will never take a lock to write to the
+ring buffer. This means we only need to worry about a single reader,
+and writes only preempt in "stack" formation.
+
+When the reader tries to swap the page with the ring buffer, it
+will also use cmpxchg. If the flag bit in the pointer to the
+head page does not have the HEADER flag set, the compare will fail
+and the reader will need to look for the new head page and try again.
+Note, the flags UPDATE and HEADER are never set at the same time.
+
+The reader swaps the reader page as follows:
+
+  +------+
+  |reader|          RING BUFFER
+  |page  |
+  +------+
+                  +---+    +---+    +---+
+                  |   |--->|   |--->|   |
+                  |   |<---|   |<---|   |
+                  +---+    +---+    +---+
+                   ^ |               ^ |
+                   | +---------------+ |
+                   +-----H-------------+
+
+The reader sets the reader page next pointer as HEADER to the page after
+the head page.
+
+
+  +------+
+  |reader|          RING BUFFER
+  |page  |-------H-----------+
+  +------+                   v
+    |             +---+    +---+    +---+
+    |             |   |--->|   |--->|   |
+    |             |   |<---|   |<---|   |<-+
+    |             +---+    +---+    +---+  |
+    |              ^ |               ^ |   |
+    |              | +---------------+ |   |
+    |              +-----H-------------+   |
+    +--------------------------------------+
+
+It does a cmpxchg with the pointer to the previous head page to make it
+point to the reader page. Note that the new pointer does not have the HEADER
+flag set.  This action atomically moves the head page forward.
+
+  +------+
+  |reader|          RING BUFFER
+  |page  |-------H-----------+
+  +------+                   v
+    |  ^          +---+   +---+   +---+
+    |  |          |   |-->|   |-->|   |
+    |  |          |   |<--|   |<--|   |<-+
+    |  |          +---+   +---+   +---+  |
+    |  |             |             ^ |   |
+    |  |             +-------------+ |   |
+    |  +-----------------------------+   |
+    +------------------------------------+
+
+After the new head page is set, the previous pointer of the head page is
+updated to the reader page.
+
+  +------+
+  |reader|          RING BUFFER
+  |page  |-------H-----------+
+  +------+ <---------------+ v
+    |  ^          +---+   +---+   +---+
+    |  |          |   |-->|   |-->|   |
+    |  |          |   |   |   |<--|   |<-+
+    |  |          +---+   +---+   +---+  |
+    |  |             |             ^ |   |
+    |  |             +-------------+ |   |
+    |  +-----------------------------+   |
+    +------------------------------------+
+
+  +------+
+  |buffer|          RING BUFFER
+  |page  |-------H-----------+  <--- New head page
+  +------+ <---------------+ v
+    |  ^          +---+   +---+   +---+
+    |  |          |   |   |   |-->|   |
+    |  |  New     |   |   |   |<--|   |<-+
+    |  | Reader   +---+   +---+   +---+  |
+    |  |  page ----^                 |   |
+    |  |                             |   |
+    |  +-----------------------------+   |
+    +------------------------------------+
+
+Another important point: The page that the reader page points back to
+by its previous pointer (the one that now points to the new head page)
+never points back to the reader page. That is because the reader page is
+not part of the ring buffer. Traversing the ring buffer via the next pointers
+will always stay in the ring buffer. Traversing the ring buffer via the
+prev pointers may not.
+
+Note, the way to determine a reader page is simply by examining the previous
+pointer of the page. If the next pointer of the previous page does not
+point back to the original page, then the original page is a reader page:
+
+
+             +--------+
+             | reader |  next   +----+
+             |  page  |-------->|    |<====== (buffer page)
+             +--------+         +----+
+                 |                | ^
+                 |                v | next
+            prev |              +----+
+                 +------------->|    |
+                                +----+
+
+The way the head page moves forward:
+
+When the tail page meets the head page and the buffer is in overwrite mode
+and more writes take place, the head page must be moved forward before the
+writer may move the tail page. The way this is done is that the writer
+performs a cmpxchg to convert the pointer to the head page from the HEADER
+flag to have the UPDATE flag set. Once this is done, the reader will
+not be able to swap the head page from the buffer, nor will it be able to
+move the head page, until the writer is finished with the move.
+
+This eliminates any races that the reader can have on the writer. The reader
+must spin, and this is why the reader cannot preempt the writer.
+
+            tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-H->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+            tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+The following page will be made into the new head page.
+
+           tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |-H->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+After the new head page has been set, we can set the old head page
+pointer back to NORMAL.
+
+           tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |--->|   |-H->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+After the head page has been moved, the tail page may now move forward.
+
+                    tail page
+                        |
+                        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |--->|   |-H->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+
+The above are the trivial updates. Now for the more complex scenarios.
+
+
+As stated before, if enough writes preempt the first write, the
+tail page may make it all the way around the buffer and meet the commit
+page. At this time, we must start dropping writes (usually with some kind
+of warning to the user). But what happens if the commit was still on the
+reader page? The commit page is not part of the ring buffer. The tail page
+must account for this.
+
+
+          reader page    commit page
+              |              |
+              v              |
+             +---+           |
+             |   |<----------+
+             |   |
+             |   |------+
+             +---+      |
+                        |
+                        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-H->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+               ^
+               |
+           tail page
+
+If the tail page were to simply push the head page forward, the commit when
+leaving the reader page would not be pointing to the correct page.
+
+The solution to this is to test if the commit page is on the reader page
+before pushing the head page. If it is, then it can be assumed that the
+tail page wrapped the buffer, and we must drop new writes.
+
+This is not a race condition, because the commit page can only be moved
+by the outermost writer (the writer that was preempted).
+This means that the commit will not move while a writer is moving the
+tail page. The reader cannot swap the reader page if it is also being
+used as the commit page. The reader can simply check that the commit
+is off the reader page. Once the commit page leaves the reader page
+it will never go back on it unless a reader does another swap with the
+buffer page that is also the commit page.
+
+
+Nested writes
+-------------
+
+In the pushing forward of the tail page we must first push forward
+the head page if the head page is the next page. If the head page
+is not the next page, the tail page is simply updated with a cmpxchg.
+
+Only writers move the tail page. This must be done atomically to protect
+against nested writers.
+
+  temp_page = tail_page
+  next_page = temp_page->next
+  cmpxchg(tail_page, temp_page, next_page)
+
+The above will update the tail page if it is still pointing to the expected
+page. If this fails, a nested write pushed it forward, the current write
+does not need to push it.
+
+
+           temp page
+               |
+               v
+            tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |--->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+Nested write comes in and moves the tail page forward:
+
+                    tail page (moved by nested writer)
+            temp page   |
+               |        |
+               v        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |--->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+The above would fail the cmpxchg, but since the tail page has already
+been moved forward, the writer will just try again to reserve storage
+on the new tail page.
+
+But the moving of the head page is a bit more complex.
+
+            tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-H->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+The write converts the head page pointer to UPDATE.
+
+            tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+But if a nested writer preempts here, it will see that the next
+page is a head page, but it is also nested. It will detect that
+it is nested and will save that information. The detection is the
+fact that it sees the UPDATE flag instead of a HEADER or NORMAL
+pointer.
+
+The nested writer will set the new head page pointer.
+
+           tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |-H->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+But it will not reset the update back to normal. Only the writer
+that converted a pointer from HEAD to UPDATE will convert it back
+to NORMAL.
+
+                    tail page
+                        |
+                        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |-H->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+After the nested writer finishes, the outermost writer will convert
+the UPDATE pointer to NORMAL.
+
+
+                    tail page
+                        |
+                        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |--->|   |-H->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+
+It can be even more complex if several nested writes came in and moved
+the tail page ahead several pages:
+
+
+(first writer)
+
+            tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-H->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+The write converts the head page pointer to UPDATE.
+
+            tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |--->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+Next writer comes in, and sees the update and sets up the new
+head page.
+
+(second writer)
+
+           tail page
+               |
+               v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |-H->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+The nested writer moves the tail page forward. But does not set the old
+update page to NORMAL because it is not the outermost writer.
+
+                    tail page
+                        |
+                        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |-H->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+Another writer preempts and sees the page after the tail page is a head page.
+It changes it from HEAD to UPDATE.
+
+(third writer)
+
+                    tail page
+                        |
+                        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |-U->|   |--->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+The writer will move the head page forward:
+
+
+(third writer)
+
+                    tail page
+                        |
+                        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |-U->|   |-H->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+But now that the third writer did change the HEAD flag to UPDATE it
+will convert it to normal:
+
+
+(third writer)
+
+                    tail page
+                        |
+                        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |--->|   |-H->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+
+Then it will move the tail page, and return back to the second writer.
+
+
+(second writer)
+
+                             tail page
+                                 |
+                                 v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |--->|   |-H->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+
+The second writer will fail to move the tail page because it was already
+moved, so it will try again and add its data to the new tail page.
+It will return to the first writer.
+
+
+(first writer)
+
+                             tail page
+                                 |
+                                 v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |--->|   |-H->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+The first writer cannot know atomically if the tail page moved
+while it updates the HEAD page. It will then update the head page to
+what it thinks is the new head page.
+
+
+(first writer)
+
+                             tail page
+                                 |
+                                 v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |-H->|   |-H->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+Since the cmpxchg returns the old value of the pointer the first writer
+will see it succeeded in updating the pointer from NORMAL to HEAD.
+But as we can see, this is not good enough. It must also check to see
+if the tail page is either where it use to be or on the next page:
+
+
+(first writer)
+
+               A        B    tail page
+               |        |        |
+               v        v        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |-H->|   |-H->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+If tail page != A and tail page != B, then it must reset the pointer
+back to NORMAL. The fact that it only needs to worry about nested
+writers means that it only needs to check this after setting the HEAD page.
+
+
+(first writer)
+
+               A        B    tail page
+               |        |        |
+               v        v        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |-U->|   |--->|   |-H->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
+Now the writer can update the head page. This is also why the head page must
+remain in UPDATE and only reset by the outermost writer. This prevents
+the reader from seeing the incorrect head page.
+
+
+(first writer)
+
+               A        B    tail page
+               |        |        |
+               v        v        v
+    +---+    +---+    +---+    +---+
+<---|   |--->|   |--->|   |--->|   |-H->
+--->|   |<---|   |<---|   |<---|   |<---
+    +---+    +---+    +---+    +---+
+
diff --git a/Documentation/trace/tracepoint-analysis.txt b/Documentation/trace/tracepoint-analysis.txt
new file mode 100644
index 000000000..058cc6c9d
--- /dev/null
+++ b/Documentation/trace/tracepoint-analysis.txt
@@ -0,0 +1,327 @@
+		Notes on Analysing Behaviour Using Events and Tracepoints
+
+			Documentation written by Mel Gorman
+		PCL information heavily based on email from Ingo Molnar
+
+1. Introduction
+===============
+
+Tracepoints (see Documentation/trace/tracepoints.txt) can be used without
+creating custom kernel modules to register probe functions using the event
+tracing infrastructure.
+
+Simplistically, tracepoints represent important events that can be
+taken in conjunction with other tracepoints to build a "Big Picture" of
+what is going on within the system. There are a large number of methods for
+gathering and interpreting these events. Lacking any current Best Practises,
+this document describes some of the methods that can be used.
+
+This document assumes that debugfs is mounted on /sys/kernel/debug and that
+the appropriate tracing options have been configured into the kernel. It is
+assumed that the PCL tool tools/perf has been installed and is in your path.
+
+2. Listing Available Events
+===========================
+
+2.1 Standard Utilities
+----------------------
+
+All possible events are visible from /sys/kernel/debug/tracing/events. Simply
+calling
+
+  $ find /sys/kernel/debug/tracing/events -type d
+
+will give a fair indication of the number of events available.
+
+2.2 PCL (Performance Counters for Linux)
+-------
+
+Discovery and enumeration of all counters and events, including tracepoints,
+are available with the perf tool. Getting a list of available events is a
+simple case of:
+
+  $ perf list 2>&1 | grep Tracepoint
+  ext4:ext4_free_inode                     [Tracepoint event]
+  ext4:ext4_request_inode                  [Tracepoint event]
+  ext4:ext4_allocate_inode                 [Tracepoint event]
+  ext4:ext4_write_begin                    [Tracepoint event]
+  ext4:ext4_ordered_write_end              [Tracepoint event]
+  [ .... remaining output snipped .... ]
+
+
+3. Enabling Events
+==================
+
+3.1 System-Wide Event Enabling
+------------------------------
+
+See Documentation/trace/events.txt for a proper description on how events
+can be enabled system-wide. A short example of enabling all events related
+to page allocation would look something like:
+
+  $ for i in `find /sys/kernel/debug/tracing/events -name "enable" | grep mm_`; do echo 1 > $i; done
+
+3.2 System-Wide Event Enabling with SystemTap
+---------------------------------------------
+
+In SystemTap, tracepoints are accessible using the kernel.trace() function
+call. The following is an example that reports every 5 seconds what processes
+were allocating the pages.
+
+  global page_allocs
+
+  probe kernel.trace("mm_page_alloc") {
+  	page_allocs[execname()]++
+  }
+
+  function print_count() {
+  	printf ("%-25s %-s\n", "#Pages Allocated", "Process Name")
+  	foreach (proc in page_allocs-)
+  		printf("%-25d %s\n", page_allocs[proc], proc)
+  	printf ("\n")
+  	delete page_allocs
+  }
+
+  probe timer.s(5) {
+          print_count()
+  }
+
+3.3 System-Wide Event Enabling with PCL
+---------------------------------------
+
+By specifying the -a switch and analysing sleep, the system-wide events
+for a duration of time can be examined.
+
+ $ perf stat -a \
+	-e kmem:mm_page_alloc -e kmem:mm_page_free \
+	-e kmem:mm_page_free_batched \
+	sleep 10
+ Performance counter stats for 'sleep 10':
+
+           9630  kmem:mm_page_alloc
+           2143  kmem:mm_page_free
+           7424  kmem:mm_page_free_batched
+
+   10.002577764  seconds time elapsed
+
+Similarly, one could execute a shell and exit it as desired to get a report
+at that point.
+
+3.4 Local Event Enabling
+------------------------
+
+Documentation/trace/ftrace.txt describes how to enable events on a per-thread
+basis using set_ftrace_pid.
+
+3.5 Local Event Enablement with PCL
+-----------------------------------
+
+Events can be activated and tracked for the duration of a process on a local
+basis using PCL such as follows.
+
+  $ perf stat -e kmem:mm_page_alloc -e kmem:mm_page_free \
+		 -e kmem:mm_page_free_batched ./hackbench 10
+  Time: 0.909
+
+    Performance counter stats for './hackbench 10':
+
+          17803  kmem:mm_page_alloc
+          12398  kmem:mm_page_free
+           4827  kmem:mm_page_free_batched
+
+    0.973913387  seconds time elapsed
+
+4. Event Filtering
+==================
+
+Documentation/trace/ftrace.txt covers in-depth how to filter events in
+ftrace.  Obviously using grep and awk of trace_pipe is an option as well
+as any script reading trace_pipe.
+
+5. Analysing Event Variances with PCL
+=====================================
+
+Any workload can exhibit variances between runs and it can be important
+to know what the standard deviation is. By and large, this is left to the
+performance analyst to do it by hand. In the event that the discrete event
+occurrences are useful to the performance analyst, then perf can be used.
+
+  $ perf stat --repeat 5 -e kmem:mm_page_alloc -e kmem:mm_page_free
+			-e kmem:mm_page_free_batched ./hackbench 10
+  Time: 0.890
+  Time: 0.895
+  Time: 0.915
+  Time: 1.001
+  Time: 0.899
+
+   Performance counter stats for './hackbench 10' (5 runs):
+
+          16630  kmem:mm_page_alloc         ( +-   3.542% )
+          11486  kmem:mm_page_free	    ( +-   4.771% )
+           4730  kmem:mm_page_free_batched  ( +-   2.325% )
+
+    0.982653002  seconds time elapsed   ( +-   1.448% )
+
+In the event that some higher-level event is required that depends on some
+aggregation of discrete events, then a script would need to be developed.
+
+Using --repeat, it is also possible to view how events are fluctuating over
+time on a system-wide basis using -a and sleep.
+
+  $ perf stat -e kmem:mm_page_alloc -e kmem:mm_page_free \
+		-e kmem:mm_page_free_batched \
+		-a --repeat 10 \
+		sleep 1
+  Performance counter stats for 'sleep 1' (10 runs):
+
+           1066  kmem:mm_page_alloc         ( +-  26.148% )
+            182  kmem:mm_page_free          ( +-   5.464% )
+            890  kmem:mm_page_free_batched  ( +-  30.079% )
+
+    1.002251757  seconds time elapsed   ( +-   0.005% )
+
+6. Higher-Level Analysis with Helper Scripts
+============================================
+
+When events are enabled the events that are triggering can be read from
+/sys/kernel/debug/tracing/trace_pipe in human-readable format although binary
+options exist as well. By post-processing the output, further information can
+be gathered on-line as appropriate. Examples of post-processing might include
+
+  o Reading information from /proc for the PID that triggered the event
+  o Deriving a higher-level event from a series of lower-level events.
+  o Calculating latencies between two events
+
+Documentation/trace/postprocess/trace-pagealloc-postprocess.pl is an example
+script that can read trace_pipe from STDIN or a copy of a trace. When used
+on-line, it can be interrupted once to generate a report without exiting
+and twice to exit.
+
+Simplistically, the script just reads STDIN and counts up events but it
+also can do more such as
+
+  o Derive high-level events from many low-level events. If a number of pages
+    are freed to the main allocator from the per-CPU lists, it recognises
+    that as one per-CPU drain even though there is no specific tracepoint
+    for that event
+  o It can aggregate based on PID or individual process number
+  o In the event memory is getting externally fragmented, it reports
+    on whether the fragmentation event was severe or moderate.
+  o When receiving an event about a PID, it can record who the parent was so
+    that if large numbers of events are coming from very short-lived
+    processes, the parent process responsible for creating all the helpers
+    can be identified
+
+7. Lower-Level Analysis with PCL
+================================
+
+There may also be a requirement to identify what functions within a program
+were generating events within the kernel. To begin this sort of analysis, the
+data must be recorded. At the time of writing, this required root:
+
+  $ perf record -c 1 \
+	-e kmem:mm_page_alloc -e kmem:mm_page_free \
+	-e kmem:mm_page_free_batched \
+	./hackbench 10
+  Time: 0.894
+  [ perf record: Captured and wrote 0.733 MB perf.data (~32010 samples) ]
+
+Note the use of '-c 1' to set the event period to sample. The default sample
+period is quite high to minimise overhead but the information collected can be
+very coarse as a result.
+
+This record outputted a file called perf.data which can be analysed using
+perf report.
+
+  $ perf report
+  # Samples: 30922
+  #
+  # Overhead    Command                     Shared Object
+  # ........  .........  ................................
+  #
+      87.27%  hackbench  [vdso]
+       6.85%  hackbench  /lib/i686/cmov/libc-2.9.so
+       2.62%  hackbench  /lib/ld-2.9.so
+       1.52%       perf  [vdso]
+       1.22%  hackbench  ./hackbench
+       0.48%  hackbench  [kernel]
+       0.02%       perf  /lib/i686/cmov/libc-2.9.so
+       0.01%       perf  /usr/bin/perf
+       0.01%       perf  /lib/ld-2.9.so
+       0.00%  hackbench  /lib/i686/cmov/libpthread-2.9.so
+  #
+  # (For more details, try: perf report --sort comm,dso,symbol)
+  #
+
+According to this, the vast majority of events triggered on events
+within the VDSO. With simple binaries, this will often be the case so let's
+take a slightly different example. In the course of writing this, it was
+noticed that X was generating an insane amount of page allocations so let's look
+at it:
+
+  $ perf record -c 1 -f \
+		-e kmem:mm_page_alloc -e kmem:mm_page_free \
+		-e kmem:mm_page_free_batched \
+		-p `pidof X`
+
+This was interrupted after a few seconds and
+
+  $ perf report
+  # Samples: 27666
+  #
+  # Overhead  Command                            Shared Object
+  # ........  .......  .......................................
+  #
+      51.95%     Xorg  [vdso]
+      47.95%     Xorg  /opt/gfx-test/lib/libpixman-1.so.0.13.1
+       0.09%     Xorg  /lib/i686/cmov/libc-2.9.so
+       0.01%     Xorg  [kernel]
+  #
+  # (For more details, try: perf report --sort comm,dso,symbol)
+  #
+
+So, almost half of the events are occurring in a library. To get an idea which
+symbol:
+
+  $ perf report --sort comm,dso,symbol
+  # Samples: 27666
+  #
+  # Overhead  Command                            Shared Object  Symbol
+  # ........  .......  .......................................  ......
+  #
+      51.95%     Xorg  [vdso]                                   [.] 0x000000ffffe424
+      47.93%     Xorg  /opt/gfx-test/lib/libpixman-1.so.0.13.1  [.] pixmanFillsse2
+       0.09%     Xorg  /lib/i686/cmov/libc-2.9.so               [.] _int_malloc
+       0.01%     Xorg  /opt/gfx-test/lib/libpixman-1.so.0.13.1  [.] pixman_region32_copy_f
+       0.01%     Xorg  [kernel]                                 [k] read_hpet
+       0.01%     Xorg  /opt/gfx-test/lib/libpixman-1.so.0.13.1  [.] get_fast_path
+       0.00%     Xorg  [kernel]                                 [k] ftrace_trace_userstack
+
+To see where within the function pixmanFillsse2 things are going wrong:
+
+  $ perf annotate pixmanFillsse2
+  [ ... ]
+    0.00 :         34eeb:       0f 18 08                prefetcht0 (%eax)
+         :      }
+         :
+         :      extern __inline void __attribute__((__gnu_inline__, __always_inline__, _
+         :      _mm_store_si128 (__m128i *__P, __m128i __B) :      {
+         :        *__P = __B;
+   12.40 :         34eee:       66 0f 7f 80 40 ff ff    movdqa %xmm0,-0xc0(%eax)
+    0.00 :         34ef5:       ff
+   12.40 :         34ef6:       66 0f 7f 80 50 ff ff    movdqa %xmm0,-0xb0(%eax)
+    0.00 :         34efd:       ff
+   12.39 :         34efe:       66 0f 7f 80 60 ff ff    movdqa %xmm0,-0xa0(%eax)
+    0.00 :         34f05:       ff
+   12.67 :         34f06:       66 0f 7f 80 70 ff ff    movdqa %xmm0,-0x90(%eax)
+    0.00 :         34f0d:       ff
+   12.58 :         34f0e:       66 0f 7f 40 80          movdqa %xmm0,-0x80(%eax)
+   12.31 :         34f13:       66 0f 7f 40 90          movdqa %xmm0,-0x70(%eax)
+   12.40 :         34f18:       66 0f 7f 40 a0          movdqa %xmm0,-0x60(%eax)
+   12.31 :         34f1d:       66 0f 7f 40 b0          movdqa %xmm0,-0x50(%eax)
+
+At a glance, it looks like the time is being spent copying pixmaps to
+the card.  Further investigation would be needed to determine why pixmaps
+are being copied around so much but a starting point would be to take an
+ancient build of libpixmap out of the library path where it was totally
+forgotten about from months ago!
diff --git a/Documentation/trace/tracepoints.txt b/Documentation/trace/tracepoints.txt
new file mode 100644
index 000000000..a3efac621
--- /dev/null
+++ b/Documentation/trace/tracepoints.txt
@@ -0,0 +1,145 @@
+	             Using the Linux Kernel Tracepoints
+
+			    Mathieu Desnoyers
+
+
+This document introduces Linux Kernel Tracepoints and their use. It
+provides examples of how to insert tracepoints in the kernel and
+connect probe functions to them and provides some examples of probe
+functions.
+
+
+* Purpose of tracepoints
+
+A tracepoint placed in code provides a hook to call a function (probe)
+that you can provide at runtime. A tracepoint can be "on" (a probe is
+connected to it) or "off" (no probe is attached). When a tracepoint is
+"off" it has no effect, except for adding a tiny time penalty
+(checking a condition for a branch) and space penalty (adding a few
+bytes for the function call at the end of the instrumented function
+and adds a data structure in a separate section).  When a tracepoint
+is "on", the function you provide is called each time the tracepoint
+is executed, in the execution context of the caller. When the function
+provided ends its execution, it returns to the caller (continuing from
+the tracepoint site).
+
+You can put tracepoints at important locations in the code. They are
+lightweight hooks that can pass an arbitrary number of parameters,
+which prototypes are described in a tracepoint declaration placed in a
+header file.
+
+They can be used for tracing and performance accounting.
+
+
+* Usage
+
+Two elements are required for tracepoints :
+
+- A tracepoint definition, placed in a header file.
+- The tracepoint statement, in C code.
+
+In order to use tracepoints, you should include linux/tracepoint.h.
+
+In include/trace/events/subsys.h :
+
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM subsys
+
+#if !defined(_TRACE_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_SUBSYS_H
+
+#include <linux/tracepoint.h>
+
+DECLARE_TRACE(subsys_eventname,
+	TP_PROTO(int firstarg, struct task_struct *p),
+	TP_ARGS(firstarg, p));
+
+#endif /* _TRACE_SUBSYS_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
+
+In subsys/file.c (where the tracing statement must be added) :
+
+#include <trace/events/subsys.h>
+
+#define CREATE_TRACE_POINTS
+DEFINE_TRACE(subsys_eventname);
+
+void somefct(void)
+{
+	...
+	trace_subsys_eventname(arg, task);
+	...
+}
+
+Where :
+- subsys_eventname is an identifier unique to your event
+    - subsys is the name of your subsystem.
+    - eventname is the name of the event to trace.
+
+- TP_PROTO(int firstarg, struct task_struct *p) is the prototype of the
+  function called by this tracepoint.
+
+- TP_ARGS(firstarg, p) are the parameters names, same as found in the
+  prototype.
+
+- if you use the header in multiple source files, #define CREATE_TRACE_POINTS
+  should appear only in one source file.
+
+Connecting a function (probe) to a tracepoint is done by providing a
+probe (function to call) for the specific tracepoint through
+register_trace_subsys_eventname().  Removing a probe is done through
+unregister_trace_subsys_eventname(); it will remove the probe.
+
+tracepoint_synchronize_unregister() must be called before the end of
+the module exit function to make sure there is no caller left using
+the probe. This, and the fact that preemption is disabled around the
+probe call, make sure that probe removal and module unload are safe.
+
+The tracepoint mechanism supports inserting multiple instances of the
+same tracepoint, but a single definition must be made of a given
+tracepoint name over all the kernel to make sure no type conflict will
+occur. Name mangling of the tracepoints is done using the prototypes
+to make sure typing is correct. Verification of probe type correctness
+is done at the registration site by the compiler. Tracepoints can be
+put in inline functions, inlined static functions, and unrolled loops
+as well as regular functions.
+
+The naming scheme "subsys_event" is suggested here as a convention
+intended to limit collisions. Tracepoint names are global to the
+kernel: they are considered as being the same whether they are in the
+core kernel image or in modules.
+
+If the tracepoint has to be used in kernel modules, an
+EXPORT_TRACEPOINT_SYMBOL_GPL() or EXPORT_TRACEPOINT_SYMBOL() can be
+used to export the defined tracepoints.
+
+If you need to do a bit of work for a tracepoint parameter, and
+that work is only used for the tracepoint, that work can be encapsulated
+within an if statement with the following:
+
+	if (trace_foo_bar_enabled()) {
+		int i;
+		int tot = 0;
+
+		for (i = 0; i < count; i++)
+			tot += calculate_nuggets();
+
+		trace_foo_bar(tot);
+	}
+
+All trace_<tracepoint>() calls have a matching trace_<tracepoint>_enabled()
+function defined that returns true if the tracepoint is enabled and
+false otherwise. The trace_<tracepoint>() should always be within the
+block of the if (trace_<tracepoint>_enabled()) to prevent races between
+the tracepoint being enabled and the check being seen.
+
+The advantage of using the trace_<tracepoint>_enabled() is that it uses
+the static_key of the tracepoint to allow the if statement to be implemented
+with jump labels and avoid conditional branches.
+
+Note: The convenience macro TRACE_EVENT provides an alternative way to
+      define tracepoints. Check http://lwn.net/Articles/379903,
+      http://lwn.net/Articles/381064 and http://lwn.net/Articles/383362
+      for a series of articles with more details.
diff --git a/Documentation/trace/uprobetracer.txt b/Documentation/trace/uprobetracer.txt
new file mode 100644
index 000000000..f1cf9a34a
--- /dev/null
+++ b/Documentation/trace/uprobetracer.txt
@@ -0,0 +1,159 @@
+            Uprobe-tracer: Uprobe-based Event Tracing
+            =========================================
+
+           Documentation written by Srikar Dronamraju
+
+
+Overview
+--------
+Uprobe based trace events are similar to kprobe based trace events.
+To enable this feature, build your kernel with CONFIG_UPROBE_EVENT=y.
+
+Similar to the kprobe-event tracer, this doesn't need to be activated via
+current_tracer. Instead of that, add probe points via
+/sys/kernel/debug/tracing/uprobe_events, and enable it via
+/sys/kernel/debug/tracing/events/uprobes/<EVENT>/enabled.
+
+However unlike kprobe-event tracer, the uprobe event interface expects the
+user to calculate the offset of the probepoint in the object.
+
+Synopsis of uprobe_tracer
+-------------------------
+  p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe
+  r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe)
+  -:[GRP/]EVENT                           : Clear uprobe or uretprobe event
+
+  GRP           : Group name. If omitted, "uprobes" is the default value.
+  EVENT         : Event name. If omitted, the event name is generated based
+                  on PATH+OFFSET.
+  PATH          : Path to an executable or a library.
+  OFFSET        : Offset where the probe is inserted.
+
+  FETCHARGS     : Arguments. Each probe can have up to 128 args.
+   %REG         : Fetch register REG
+   @ADDR	: Fetch memory at ADDR (ADDR should be in userspace)
+   @+OFFSET	: Fetch memory at OFFSET (OFFSET from same file as PATH)
+   $stackN	: Fetch Nth entry of stack (N >= 0)
+   $stack	: Fetch stack address.
+   $retval	: Fetch return value.(*)
+   +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
+   NAME=FETCHARG     : Set NAME as the argument name of FETCHARG.
+   FETCHARG:TYPE     : Set TYPE as the type of FETCHARG. Currently, basic types
+		       (u8/u16/u32/u64/s8/s16/s32/s64), "string" and bitfield
+		       are supported.
+
+  (*) only for return probe.
+  (**) this is useful for fetching a field of data structures.
+
+Types
+-----
+Several types are supported for fetch-args. Uprobe tracer will access memory
+by given type. Prefix 's' and 'u' means those types are signed and unsigned
+respectively. Traced arguments are shown in decimal (signed) or hex (unsigned).
+String type is a special type, which fetches a "null-terminated" string from
+user space.
+Bitfield is another special type, which takes 3 parameters, bit-width, bit-
+offset, and container-size (usually 32). The syntax is;
+
+ b<bit-width>@<bit-offset>/<container-size>
+
+
+Event Profiling
+---------------
+You can check the total number of probe hits and probe miss-hits via
+/sys/kernel/debug/tracing/uprobe_profile.
+The first column is event name, the second is the number of probe hits,
+the third is the number of probe miss-hits.
+
+Usage examples
+--------------
+ * Add a probe as a new uprobe event, write a new definition to uprobe_events
+as below: (sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash)
+
+    echo 'p: /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events
+
+ * Add a probe as a new uretprobe event:
+
+    echo 'r: /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events
+
+ * Unset registered event:
+
+    echo '-:bash_0x4245c0' >> /sys/kernel/debug/tracing/uprobe_events
+
+ * Print out the events that are registered:
+
+    cat /sys/kernel/debug/tracing/uprobe_events
+
+ * Clear all events:
+
+    echo > /sys/kernel/debug/tracing/uprobe_events
+
+Following example shows how to dump the instruction pointer and %ax register
+at the probed text address. Probe zfree function in /bin/zsh:
+
+    # cd /sys/kernel/debug/tracing/
+    # cat /proc/`pgrep zsh`/maps | grep /bin/zsh | grep r-xp
+    00400000-0048a000 r-xp 00000000 08:03 130904 /bin/zsh
+    # objdump -T /bin/zsh | grep -w zfree
+    0000000000446420 g    DF .text  0000000000000012  Base        zfree
+
+  0x46420 is the offset of zfree in object /bin/zsh that is loaded at
+  0x00400000. Hence the command to uprobe would be:
+
+    # echo 'p:zfree_entry /bin/zsh:0x46420 %ip %ax' > uprobe_events
+
+  And the same for the uretprobe would be:
+
+    # echo 'r:zfree_exit /bin/zsh:0x46420 %ip %ax' >> uprobe_events
+
+Please note: User has to explicitly calculate the offset of the probe-point
+in the object. We can see the events that are registered by looking at the
+uprobe_events file.
+
+    # cat uprobe_events
+    p:uprobes/zfree_entry /bin/zsh:0x00046420 arg1=%ip arg2=%ax
+    r:uprobes/zfree_exit /bin/zsh:0x00046420 arg1=%ip arg2=%ax
+
+Format of events can be seen by viewing the file events/uprobes/zfree_entry/format
+
+    # cat events/uprobes/zfree_entry/format
+    name: zfree_entry
+    ID: 922
+    format:
+         field:unsigned short common_type;         offset:0;  size:2; signed:0;
+         field:unsigned char common_flags;         offset:2;  size:1; signed:0;
+         field:unsigned char common_preempt_count; offset:3;  size:1; signed:0;
+         field:int common_pid;                     offset:4;  size:4; signed:1;
+         field:int common_padding;                 offset:8;  size:4; signed:1;
+
+         field:unsigned long __probe_ip;           offset:12; size:4; signed:0;
+         field:u32 arg1;                           offset:16; size:4; signed:0;
+         field:u32 arg2;                           offset:20; size:4; signed:0;
+
+    print fmt: "(%lx) arg1=%lx arg2=%lx", REC->__probe_ip, REC->arg1, REC->arg2
+
+Right after definition, each event is disabled by default. For tracing these
+events, you need to enable it by:
+
+    # echo 1 > events/uprobes/enable
+
+Lets disable the event after sleeping for some time.
+
+    # sleep 20
+    # echo 0 > events/uprobes/enable
+
+And you can see the traced information via /sys/kernel/debug/tracing/trace.
+
+    # cat trace
+    # tracer: nop
+    #
+    #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
+    #              | |       |          |         |
+                 zsh-24842 [006] 258544.995456: zfree_entry: (0x446420) arg1=446420 arg2=79
+                 zsh-24842 [007] 258545.000270: zfree_exit:  (0x446540 <- 0x446420) arg1=446540 arg2=0
+                 zsh-24842 [002] 258545.043929: zfree_entry: (0x446420) arg1=446420 arg2=79
+                 zsh-24842 [004] 258547.046129: zfree_exit:  (0x446540 <- 0x446420) arg1=446540 arg2=0
+
+Output shows us uprobe was triggered for a pid 24842 with ip being 0x446420
+and contents of ax register being 79. And uretprobe was triggered with ip at
+0x446540 with counterpart function entry at 0x446420.