diff options
Diffstat (limited to 'Documentation/RCU')
| -rw-r--r-- | Documentation/RCU/rcu_dereference.txt | 2 | ||||
| -rw-r--r-- | Documentation/RCU/stallwarn.txt | 29 | ||||
| -rw-r--r-- | Documentation/RCU/trace.txt | 36 | ||||
| -rw-r--r-- | Documentation/RCU/whatisRCU.txt | 2 |
4 files changed, 31 insertions, 38 deletions
diff --git a/Documentation/RCU/rcu_dereference.txt b/Documentation/RCU/rcu_dereference.txt index 1e6c0da99..c0bf2441a 100644 --- a/Documentation/RCU/rcu_dereference.txt +++ b/Documentation/RCU/rcu_dereference.txt @@ -28,7 +28,7 @@ o You must use one of the rcu_dereference() family of primitives o Avoid cancellation when using the "+" and "-" infix arithmetic operators. For example, for a given variable "x", avoid "(x-x)". There are similar arithmetic pitfalls from other - arithmetic operatiors, such as "(x*0)", "(x/(x+1))" or "(x%1)". + arithmetic operators, such as "(x*0)", "(x/(x+1))" or "(x%1)". The compiler is within its rights to substitute zero for all of these expressions, so that subsequent accesses no longer depend on the rcu_dereference(), again possibly resulting in bugs due diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt index b57c0c1cd..efb945487 100644 --- a/Documentation/RCU/stallwarn.txt +++ b/Documentation/RCU/stallwarn.txt @@ -26,12 +26,6 @@ CONFIG_RCU_CPU_STALL_TIMEOUT Stall-warning messages may be enabled and disabled completely via /sys/module/rcupdate/parameters/rcu_cpu_stall_suppress. -CONFIG_RCU_CPU_STALL_INFO - - This kernel configuration parameter causes the stall warning to - print out additional per-CPU diagnostic information, including - information on scheduling-clock ticks and RCU's idle-CPU tracking. - RCU_STALL_DELAY_DELTA Although the lockdep facility is extremely useful, it does add @@ -101,15 +95,13 @@ interact. Please note that it is not possible to entirely eliminate this sort of false positive without resorting to things like stop_machine(), which is overkill for this sort of problem. -If the CONFIG_RCU_CPU_STALL_INFO kernel configuration parameter is set, -more information is printed with the stall-warning message, for example: +Recent kernels will print a long form of the stall-warning message: INFO: rcu_preempt detected stall on CPU 0: (63959 ticks this GP) idle=241/3fffffffffffffff/0 softirq=82/543 (t=65000 jiffies) -In kernels with CONFIG_RCU_FAST_NO_HZ, even more information is -printed: +In kernels with CONFIG_RCU_FAST_NO_HZ, more information is printed: INFO: rcu_preempt detected stall on CPU 0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 softirq=82/543 last_accelerate: a345/d342 nonlazy_posted: 25 .D @@ -171,6 +163,23 @@ message will be about three times the interval between the beginning of the stall and the first message. +Stall Warnings for Expedited Grace Periods + +If an expedited grace period detects a stall, it will place a message +like the following in dmesg: + + INFO: rcu_sched detected expedited stalls on CPUs: { 1 2 6 } 26009 jiffies s: 1043 + +This indicates that CPUs 1, 2, and 6 have failed to respond to a +reschedule IPI, that the expedited grace period has been going on for +26,009 jiffies, and that the expedited grace-period sequence counter is +1043. The fact that this last value is odd indicates that an expedited +grace period is in flight. + +It is entirely possible to see stall warnings from normal and from +expedited grace periods at about the same time from the same run. + + What Causes RCU CPU Stall Warnings? So your kernel printed an RCU CPU stall warning. The next question is diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt index 08651da15..97f17e9de 100644 --- a/Documentation/RCU/trace.txt +++ b/Documentation/RCU/trace.txt @@ -237,42 +237,26 @@ o "ktl" is the low-order 16 bits (in hexadecimal) of the count of The output of "cat rcu/rcu_preempt/rcuexp" looks as follows: -s=21872 d=21872 w=0 tf=0 wd1=0 wd2=0 n=0 sc=21872 dt=21872 dl=0 dx=21872 +s=21872 wd0=0 wd1=0 wd2=0 wd3=5 n=0 enq=0 sc=21872 These fields are as follows: -o "s" is the starting sequence number. +o "s" is the sequence number, with an odd number indicating that + an expedited grace period is in progress. -o "d" is the ending sequence number. When the starting and ending - numbers differ, there is an expedited grace period in progress. - -o "w" is the number of times that the sequence numbers have been - in danger of wrapping. - -o "tf" is the number of times that contention has resulted in a - failure to begin an expedited grace period. - -o "wd1" and "wd2" are the number of times that an attempt to - start an expedited grace period found that someone else had - completed an expedited grace period that satisfies the +o "wd0", "wd1", "wd2", and "wd3" are the number of times that an + attempt to start an expedited grace period found that someone + else had completed an expedited grace period that satisfies the attempted request. "Our work is done." -o "n" is number of times that contention was so great that - the request was demoted from an expedited grace period to - a normal grace period. +o "n" is number of times that a concurrent CPU-hotplug operation + forced a fallback to a normal grace period. + +o "enq" is the number of quiescent states still outstanding. o "sc" is the number of times that the attempt to start a new expedited grace period succeeded. -o "dt" is the number of times that we attempted to update - the "d" counter. - -o "dl" is the number of times that we failed to update the "d" - counter. - -o "dx" is the number of times that we succeeded in updating - the "d" counter. - The output of "cat rcu/rcu_preempt/rcugp" looks as follows: diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index 5746b0c77..adc218400 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -883,7 +883,7 @@ All: lockdep-checked RCU-protected pointer access rcu_access_pointer rcu_dereference_raw - rcu_lockdep_assert + RCU_LOCKDEP_WARN rcu_sleep_check RCU_NONIDLE |