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/thread_siblings:
  24
  25         internal kernel map of cpuX's hardware threads within the same
  26         core as cpuX.
  27
  28 5) /sys/devices/system/cpu/cpuX/topology/thread_siblings_list:
  29
  30         human-readable list of cpuX's hardware threads within the same
  31         core as cpuX.
  32
  33 6) /sys/devices/system/cpu/cpuX/topology/core_siblings:
  34
  35         internal kernel map of cpuX's hardware threads within the same
  36         physical_package_id.
  37
  38 7) /sys/devices/system/cpu/cpuX/topology/core_siblings_list:
  39
  40         human-readable list of cpuX's hardware threads within the same
  41         physical_package_id.
  42
  43 8) /sys/devices/system/cpu/cpuX/topology/book_siblings:
  44
  45         internal kernel map of cpuX's hardware threads within the same
  46         book_id.
  47
  48 9) /sys/devices/system/cpu/cpuX/topology/book_siblings_list:
  49
  50         human-readable list of cpuX's hardware threads within the same
  51         book_id.
  52
  53 To implement it in an architecture-neutral way, a new source file,
  54 drivers/base/topology.c, is to export the 6 or 9 attributes. The three book
  55 related sysfs files will only be created if CONFIG_SCHED_BOOK is selected.
  56
  57 For an architecture to support this feature, it must define some of
  58 these macros in include/asm-XXX/topology.h:
  59 #define topology_physical_package_id(cpu)
  60 #define topology_core_id(cpu)
  61 #define topology_book_id(cpu)
  62 #define topology_sibling_cpumask(cpu)
  63 #define topology_core_cpumask(cpu)
  64 #define topology_book_cpumask(cpu)
  65
  66 The type of **_id macros is int.
  67 The type of **_cpumask macros is (const) struct cpumask *. The latter
  68 correspond with appropriate **_siblings sysfs attributes (except for
  69 topology_sibling_cpumask() which corresponds with thread_siblings).
  70
  71 To be consistent on all architectures, include/linux/topology.h
  72 provides default definitions for any of the above macros that are
  73 not defined by include/asm-XXX/topology.h:
  74 1) physical_package_id: -1
  75 2) core_id: 0
  76 3) sibling_cpumask: just the given CPU
  77 4) core_cpumask: just the given CPU
  78
  79 For architectures that don't support books (CONFIG_SCHED_BOOK) there are no
  80 default definitions for topology_book_id() and topology_book_cpumask().
  81
  82 Additionally, CPU topology information is provided under
  83 /sys/devices/system/cpu and includes these files.  The internal
  84 source for the output is in brackets ("[]").
  85
  86     kernel_max: the maximum CPU index allowed by the kernel configuration.
  87                 [NR_CPUS-1]
  88
  89     offline:    CPUs that are not online because they have been
  90                 HOTPLUGGED off (see cpu-hotplug.txt) or exceed the limit
  91                 of CPUs allowed by the kernel configuration (kernel_max
  92                 above). [~cpu_online_mask + cpus >= NR_CPUS]
  93
  94     online:     CPUs that are online and being scheduled [cpu_online_mask]
  95
  96     possible:   CPUs that have been allocated resources and can be
  97                 brought online if they are present. [cpu_possible_mask]
  98
  99     present:    CPUs that have been identified as being present in the
 100                 system. [cpu_present_mask]
 101
 102 The format for the above output is compatible with cpulist_parse()
 103 [see <linux/cpumask.h>].  Some examples follow.
 104
 105 In this example, there are 64 CPUs in the system but cpus 32-63 exceed
 106 the kernel max which is limited to 0..31 by the NR_CPUS config option
 107 being 32.  Note also that CPUs 2 and 4-31 are not online but could be
 108 brought online as they are both present and possible.
 109
 110      kernel_max: 31
 111         offline: 2,4-31,32-63
 112          online: 0-1,3
 113        possible: 0-31
 114         present: 0-31
 115
 116 In this example, the NR_CPUS config option is 128, but the kernel was
 117 started with possible_cpus=144.  There are 4 CPUs in the system and cpu2
 118 was manually taken offline (and is the only CPU that can be brought
 119 online.)
 120
 121      kernel_max: 127
 122         offline: 2,4-127,128-143
 123          online: 0-1,3
 124        possible: 0-127
 125         present: 0-3
 126
 127 See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter
 128 as well as more information on the various cpumasks.