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159 lines
5.6 KiB
Text
159 lines
5.6 KiB
Text
===========================================
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How CPU topology info is exported via sysfs
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===========================================
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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/drawer_id:
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the drawer 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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5) /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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6) /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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7) /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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8) /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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9) /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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10) /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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11) /sys/devices/system/cpu/cpuX/topology/drawer_siblings:
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internal kernel map of cpuX's hardware threads within the same
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drawer_id.
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12) /sys/devices/system/cpu/cpuX/topology/drawer_siblings_list:
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human-readable list of cpuX's hardware threads within the same
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drawer_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 to 12 attributes. The book
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and drawer related sysfs files will only be created if CONFIG_SCHED_BOOK
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and CONFIG_SCHED_DRAWER are selected.
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CONFIG_SCHED_BOOK and CONFIG_DRAWER are currently only used on s390, where
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they reflect the cpu and cache hierarchy.
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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_drawer_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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#define topology_drawer_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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For architectures that don't support drawers (CONFIG_SCHED_DRAWER) there are
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no default definitions for topology_drawer_id() and topology_drawer_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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=========== ==========================================================
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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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=========== ==========================================================
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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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