Documentation/cputopology.txt

   1
   2 Export CPU topology info via sysfs. Items (attributes) are similar
   3 to /proc/cpuinfo output of some architectures:
   4
   5 1) /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
  11 2) /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
  17 3) /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
  23 4) /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
  29 5) /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
  34 6) /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
  39 7) /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
  44 8) /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
  49 9) /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
  54 10) /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
  59 11) /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
  64 12) /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
  69 To implement it in an architecture-neutral way, a new source file,
  70 drivers/base/topology.c, is to export the 6 to 12 attributes. The book
  71 and drawer related sysfs files will only be created if CONFIG_SCHED_BOOK
  72 and CONFIG_SCHED_DRAWER are selected.
  73
  74 CONFIG_SCHED_BOOK and CONFIG_DRAWER are currently only used on s390, where
  75 they reflect the cpu and cache hierarchy.
  76
  77 For an architecture to support this feature, it must define some of
  78 these 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
  88 The type of **_id macros is int.
  89 The type of **_cpumask macros is (const) struct cpumask *. The latter
  90 correspond with appropriate **_siblings sysfs attributes (except for
  91 topology_sibling_cpumask() which corresponds with thread_siblings).
  92
  93 To be consistent on all architectures, include/linux/topology.h
  94 provides default definitions for any of the above macros that are
  95 not defined by include/asm-XXX/topology.h:
  96 1) physical_package_id: -1
  97 2) core_id: 0
  98 3) sibling_cpumask: just the given CPU
  99 4) core_cpumask: just the given CPU
 100
 101 For architectures that don't support books (CONFIG_SCHED_BOOK) there are no
 102 default definitions for topology_book_id() and topology_book_cpumask().
 103 For architectures that don't support drawes (CONFIG_SCHED_DRAWER) there are
 104 no default definitions for topology_drawer_id() and topology_drawer_cpumask().
 105
 106 Additionally, CPU topology information is provided under
 107 /sys/devices/system/cpu and includes these files.  The internal
 108 source 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
 126 The format for the above output is compatible with cpulist_parse()
 127 [see <linux/cpumask.h>].  Some examples follow.
 128
 129 In this example, there are 64 CPUs in the system but cpus 32-63 exceed
 130 the kernel max which is limited to 0..31 by the NR_CPUS config option
 131 being 32.  Note also that CPUs 2 and 4-31 are not online but could be
 132 brought 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
 140 In this example, the NR_CPUS config option is 128, but the kernel was
 141 started with possible_cpus=144.  There are 4 CPUs in the system and cpu2
 142 was manually taken offline (and is the only CPU that can be brought
 143 online.)
 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
 151 See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter
 152 as well as more information on the various cpumasks.