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54a5369487
The documentation on cpu topology seems to be a bit out-of-date. It doesn't mention the **_siblings_list attributes and uses old names for topology_**_cpumask() macros. Add information on missing attributes plus some additional clarifications. Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com> Cc: Benoit Cousson <bcousson@baylibre.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Fenghua Yu <fenghua.yu@intel.com> Cc: Guenter Roeck <linux@roeck-us.net> Cc: Jean Delvare <jdelvare@suse.de> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Oleg Drokin <oleg.drokin@intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rafael J. Wysocki <rjw@rjwysocki.net> Cc: Russell King <linux@arm.linux.org.uk> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Viresh Kumar <viresh.kumar@linaro.org> Link: http://lkml.kernel.org/r/1432645896-12588-3-git-send-email-bgolaszewski@baylibre.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
129 lines
4.5 KiB
Plaintext
129 lines
4.5 KiB
Plaintext
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Export CPU topology info via sysfs. Items (attributes) are similar
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to /proc/cpuinfo output of some architectures:
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1) /sys/devices/system/cpu/cpuX/topology/physical_package_id:
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physical package id of cpuX. Typically corresponds to a physical
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socket number, but the actual value is architecture and platform
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dependent.
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2) /sys/devices/system/cpu/cpuX/topology/core_id:
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the CPU core ID of cpuX. Typically it is the hardware platform's
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identifier (rather than the kernel's). The actual value is
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architecture and platform dependent.
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3) /sys/devices/system/cpu/cpuX/topology/book_id:
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the book ID of cpuX. Typically it is the hardware platform's
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identifier (rather than the kernel's). The actual value is
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architecture and platform dependent.
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4) /sys/devices/system/cpu/cpuX/topology/thread_siblings:
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internal kernel map of cpuX's hardware threads within the same
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core as cpuX.
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5) /sys/devices/system/cpu/cpuX/topology/thread_siblings_list:
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human-readable list of cpuX's hardware threads within the same
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core as cpuX.
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6) /sys/devices/system/cpu/cpuX/topology/core_siblings:
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internal kernel map of cpuX's hardware threads within the same
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physical_package_id.
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7) /sys/devices/system/cpu/cpuX/topology/core_siblings_list:
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human-readable list of cpuX's hardware threads within the same
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physical_package_id.
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8) /sys/devices/system/cpu/cpuX/topology/book_siblings:
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internal kernel map of cpuX's hardware threads within the same
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book_id.
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9) /sys/devices/system/cpu/cpuX/topology/book_siblings_list:
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human-readable list of cpuX's hardware threads within the same
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book_id.
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To implement it in an architecture-neutral way, a new source file,
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drivers/base/topology.c, is to export the 6 or 9 attributes. The three book
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related sysfs files will only be created if CONFIG_SCHED_BOOK is selected.
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For an architecture to support this feature, it must define some of
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these macros in include/asm-XXX/topology.h:
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#define topology_physical_package_id(cpu)
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#define topology_core_id(cpu)
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#define topology_book_id(cpu)
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#define topology_sibling_cpumask(cpu)
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#define topology_core_cpumask(cpu)
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#define topology_book_cpumask(cpu)
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The type of **_id macros is int.
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The type of **_cpumask macros is (const) struct cpumask *. The latter
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correspond with appropriate **_siblings sysfs attributes (except for
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topology_sibling_cpumask() which corresponds with thread_siblings).
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To be consistent on all architectures, include/linux/topology.h
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provides default definitions for any of the above macros that are
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not defined by include/asm-XXX/topology.h:
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1) physical_package_id: -1
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2) core_id: 0
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3) sibling_cpumask: just the given CPU
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4) core_cpumask: just the given CPU
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For architectures that don't support books (CONFIG_SCHED_BOOK) there are no
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default definitions for topology_book_id() and topology_book_cpumask().
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Additionally, CPU topology information is provided under
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/sys/devices/system/cpu and includes these files. The internal
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source for the output is in brackets ("[]").
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kernel_max: the maximum CPU index allowed by the kernel configuration.
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[NR_CPUS-1]
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offline: CPUs that are not online because they have been
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HOTPLUGGED off (see cpu-hotplug.txt) or exceed the limit
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of CPUs allowed by the kernel configuration (kernel_max
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above). [~cpu_online_mask + cpus >= NR_CPUS]
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online: CPUs that are online and being scheduled [cpu_online_mask]
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possible: CPUs that have been allocated resources and can be
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brought online if they are present. [cpu_possible_mask]
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present: CPUs that have been identified as being present in the
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system. [cpu_present_mask]
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The format for the above output is compatible with cpulist_parse()
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[see <linux/cpumask.h>]. Some examples follow.
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In this example, there are 64 CPUs in the system but cpus 32-63 exceed
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the kernel max which is limited to 0..31 by the NR_CPUS config option
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being 32. Note also that CPUs 2 and 4-31 are not online but could be
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brought online as they are both present and possible.
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kernel_max: 31
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offline: 2,4-31,32-63
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online: 0-1,3
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possible: 0-31
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present: 0-31
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In this example, the NR_CPUS config option is 128, but the kernel was
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started with possible_cpus=144. There are 4 CPUs in the system and cpu2
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was manually taken offline (and is the only CPU that can be brought
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online.)
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kernel_max: 127
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offline: 2,4-127,128-143
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online: 0-1,3
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possible: 0-127
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present: 0-3
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See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter
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as well as more information on the various cpumasks.
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