linux/Documentation/cputopology.txt
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   1
   2Export CPU topology info via sysfs. Items (attributes) are similar
   3to /proc/cpuinfo output of some architectures:
   4
   51) /sys/devices/system/cpu/cpuX/topology/physical_package_id:
   6
   7        physical package id of cpuX. Typically corresponds to a physical
   8        socket number, but the actual value is architecture and platform
   9        dependent.
  10
  112) /sys/devices/system/cpu/cpuX/topology/core_id:
  12
  13        the CPU core ID of cpuX. Typically it is the hardware platform's
  14        identifier (rather than the kernel's).  The actual value is
  15        architecture and platform dependent.
  16
  173) /sys/devices/system/cpu/cpuX/topology/book_id:
  18
  19        the book ID of cpuX. Typically it is the hardware platform's
  20        identifier (rather than the kernel's).  The actual value is
  21        architecture and platform dependent.
  22
  234) /sys/devices/system/cpu/cpuX/topology/drawer_id:
  24
  25        the drawer ID of cpuX. Typically it is the hardware platform's
  26        identifier (rather than the kernel's).  The actual value is
  27        architecture and platform dependent.
  28
  295) /sys/devices/system/cpu/cpuX/topology/thread_siblings:
  30
  31        internal kernel map of cpuX's hardware threads within the same
  32        core as cpuX.
  33
  346) /sys/devices/system/cpu/cpuX/topology/thread_siblings_list:
  35
  36        human-readable list of cpuX's hardware threads within the same
  37        core as cpuX.
  38
  397) /sys/devices/system/cpu/cpuX/topology/core_siblings:
  40
  41        internal kernel map of cpuX's hardware threads within the same
  42        physical_package_id.
  43
  448) /sys/devices/system/cpu/cpuX/topology/core_siblings_list:
  45
  46        human-readable list of cpuX's hardware threads within the same
  47        physical_package_id.
  48
  499) /sys/devices/system/cpu/cpuX/topology/book_siblings:
  50
  51        internal kernel map of cpuX's hardware threads within the same
  52        book_id.
  53
  5410) /sys/devices/system/cpu/cpuX/topology/book_siblings_list:
  55
  56        human-readable list of cpuX's hardware threads within the same
  57        book_id.
  58
  5911) /sys/devices/system/cpu/cpuX/topology/drawer_siblings:
  60
  61        internal kernel map of cpuX's hardware threads within the same
  62        drawer_id.
  63
  6412) /sys/devices/system/cpu/cpuX/topology/drawer_siblings_list:
  65
  66        human-readable list of cpuX's hardware threads within the same
  67        drawer_id.
  68
  69To implement it in an architecture-neutral way, a new source file,
  70drivers/base/topology.c, is to export the 6 to 12 attributes. The book
  71and drawer related sysfs files will only be created if CONFIG_SCHED_BOOK
  72and CONFIG_SCHED_DRAWER are selected.
  73
  74CONFIG_SCHED_BOOK and CONFIG_DRAWER are currently only used on s390, where
  75they reflect the cpu and cache hierarchy.
  76
  77For an architecture to support this feature, it must define some of
  78these macros in include/asm-XXX/topology.h:
  79#define topology_physical_package_id(cpu)
  80#define topology_core_id(cpu)
  81#define topology_book_id(cpu)
  82#define topology_drawer_id(cpu)
  83#define topology_sibling_cpumask(cpu)
  84#define topology_core_cpumask(cpu)
  85#define topology_book_cpumask(cpu)
  86#define topology_drawer_cpumask(cpu)
  87
  88The type of **_id macros is int.
  89The type of **_cpumask macros is (const) struct cpumask *. The latter
  90correspond with appropriate **_siblings sysfs attributes (except for
  91topology_sibling_cpumask() which corresponds with thread_siblings).
  92
  93To be consistent on all architectures, include/linux/topology.h
  94provides default definitions for any of the above macros that are
  95not defined by include/asm-XXX/topology.h:
  961) physical_package_id: -1
  972) core_id: 0
  983) sibling_cpumask: just the given CPU
  994) core_cpumask: just the given CPU
 100
 101For architectures that don't support books (CONFIG_SCHED_BOOK) there are no
 102default definitions for topology_book_id() and topology_book_cpumask().
 103For architectures that don't support drawes (CONFIG_SCHED_DRAWER) there are
 104no default definitions for topology_drawer_id() and topology_drawer_cpumask().
 105
 106Additionally, CPU topology information is provided under
 107/sys/devices/system/cpu and includes these files.  The internal
 108source for the output is in brackets ("[]").
 109
 110    kernel_max: the maximum CPU index allowed by the kernel configuration.
 111                [NR_CPUS-1]
 112
 113    offline:    CPUs that are not online because they have been
 114                HOTPLUGGED off (see cpu-hotplug.txt) or exceed the limit
 115                of CPUs allowed by the kernel configuration (kernel_max
 116                above). [~cpu_online_mask + cpus >= NR_CPUS]
 117
 118    online:     CPUs that are online and being scheduled [cpu_online_mask]
 119
 120    possible:   CPUs that have been allocated resources and can be
 121                brought online if they are present. [cpu_possible_mask]
 122
 123    present:    CPUs that have been identified as being present in the
 124                system. [cpu_present_mask]
 125
 126The format for the above output is compatible with cpulist_parse()
 127[see <linux/cpumask.h>].  Some examples follow.
 128
 129In this example, there are 64 CPUs in the system but cpus 32-63 exceed
 130the kernel max which is limited to 0..31 by the NR_CPUS config option
 131being 32.  Note also that CPUs 2 and 4-31 are not online but could be
 132brought online as they are both present and possible.
 133
 134     kernel_max: 31
 135        offline: 2,4-31,32-63
 136         online: 0-1,3
 137       possible: 0-31
 138        present: 0-31
 139
 140In this example, the NR_CPUS config option is 128, but the kernel was
 141started with possible_cpus=144.  There are 4 CPUs in the system and cpu2
 142was manually taken offline (and is the only CPU that can be brought
 143online.)
 144
 145     kernel_max: 127
 146        offline: 2,4-127,128-143
 147         online: 0-1,3
 148       possible: 0-127
 149        present: 0-3
 150
 151See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter
 152as well as more information on the various cpumasks.
 153