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+
+Export CPU topology info via sysfs. Items (attributes) are similar
+to /proc/cpuinfo.
+
+1) /sys/devices/system/cpu/cpuX/topology/physical_package_id:
+
+	physical package id of cpuX. Typically corresponds to a physical
+	socket number, but the actual value is architecture and platform
+	dependent.
+
+2) /sys/devices/system/cpu/cpuX/topology/core_id:
+
+	the CPU core ID of cpuX. Typically it is the hardware platform's
+	identifier (rather than the kernel's).  The actual value is
+	architecture and platform dependent.
+
+3) /sys/devices/system/cpu/cpuX/topology/book_id:
+
+	the book ID of cpuX. Typically it is the hardware platform's
+	identifier (rather than the kernel's).	The actual value is
+	architecture and platform dependent.
+
+4) /sys/devices/system/cpu/cpuX/topology/thread_siblings:
+
+	internal kernel map of cpuX's hardware threads within the same
+	core as cpuX
+
+5) /sys/devices/system/cpu/cpuX/topology/core_siblings:
+
+	internal kernel map of cpuX's hardware threads within the same
+	physical_package_id.
+
+6) /sys/devices/system/cpu/cpuX/topology/book_siblings:
+
+	internal kernel map of cpuX's hardware threads within the same
+	book_id.
+
+To implement it in an architecture-neutral way, a new source file,
+drivers/base/topology.c, is to export the 4 or 6 attributes. The two book
+related sysfs files will only be created if CONFIG_SCHED_BOOK is selected.
+
+For an architecture to support this feature, it must define some of
+these macros in include/asm-XXX/topology.h:
+#define topology_physical_package_id(cpu)
+#define topology_core_id(cpu)
+#define topology_book_id(cpu)
+#define topology_thread_cpumask(cpu)
+#define topology_core_cpumask(cpu)
+#define topology_book_cpumask(cpu)
+
+The type of **_id is int.
+The type of siblings is (const) struct cpumask *.
+
+To be consistent on all architectures, include/linux/topology.h
+provides default definitions for any of the above macros that are
+not defined by include/asm-XXX/topology.h:
+1) physical_package_id: -1
+2) core_id: 0
+3) thread_siblings: just the given CPU
+4) core_siblings: just the given CPU
+
+For architectures that don't support books (CONFIG_SCHED_BOOK) there are no
+default definitions for topology_book_id() and topology_book_cpumask().
+
+Additionally, CPU topology information is provided under
+/sys/devices/system/cpu and includes these files.  The internal
+source for the output is in brackets ("[]").
+
+    kernel_max: the maximum CPU index allowed by the kernel configuration.
+		[NR_CPUS-1]
+
+    offline:	CPUs that are not online because they have been
+		HOTPLUGGED off (see cpu-hotplug.txt) or exceed the limit
+		of CPUs allowed by the kernel configuration (kernel_max
+		above). [~cpu_online_mask + cpus >= NR_CPUS]
+
+    online:	CPUs that are online and being scheduled [cpu_online_mask]
+
+    possible:	CPUs that have been allocated resources and can be
+		brought online if they are present. [cpu_possible_mask]
+
+    present:	CPUs that have been identified as being present in the
+		system. [cpu_present_mask]
+
+The format for the above output is compatible with cpulist_parse()
+[see <linux/cpumask.h>].  Some examples follow.
+
+In this example, there are 64 CPUs in the system but cpus 32-63 exceed
+the kernel max which is limited to 0..31 by the NR_CPUS config option
+being 32.  Note also that CPUs 2 and 4-31 are not online but could be
+brought online as they are both present and possible.
+
+     kernel_max: 31
+        offline: 2,4-31,32-63
+         online: 0-1,3
+       possible: 0-31
+        present: 0-31
+
+In this example, the NR_CPUS config option is 128, but the kernel was
+started with possible_cpus=144.  There are 4 CPUs in the system and cpu2
+was manually taken offline (and is the only CPU that can be brought
+online.)
+
+     kernel_max: 127
+        offline: 2,4-127,128-143
+         online: 0-1,3
+       possible: 0-127
+        present: 0-3
+
+See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter
+as well as more information on the various cpumasks.