Documentation/cputopology.txt

   1
   2 Export cpu topology info via sysfs. Items (attributes) are similar
   3 to /proc/cpuinfo.
   4
   5 1) /sys/devices/system/cpu/cpuX/topology/physical_package_id:
   6 represent the physical package id of  cpu X;
   7 2) /sys/devices/system/cpu/cpuX/topology/core_id:
   8 represent the cpu core id to cpu X;
   9 3) /sys/devices/system/cpu/cpuX/topology/thread_siblings:
  10 represent the thread siblings to cpu X in the same core;
  11 4) /sys/devices/system/cpu/cpuX/topology/core_siblings:
  12 represent the thread siblings to cpu X in the same physical package;
  13
  14 To implement it in an architecture-neutral way, a new source file,
  15 drivers/base/topology.c, is to export the 4 attributes.
  16
  17 For an architecture to support this feature, it must define some of
  18 these macros in include/asm-XXX/topology.h:
  19 #define topology_physical_package_id(cpu)
  20 #define topology_core_id(cpu)
  21 #define topology_thread_cpumask(cpu)
  22 #define topology_core_cpumask(cpu)
  23
  24 The type of **_id is int.
  25 The type of siblings is (const) struct cpumask *.
  26
  27 To be consistent on all architectures, include/linux/topology.h
  28 provides default definitions for any of the above macros that are
  29 not defined by include/asm-XXX/topology.h:
  30 1) physical_package_id: -1
  31 2) core_id: 0
  32 3) thread_siblings: just the given CPU
  33 4) core_siblings: just the given CPU
  34
  35 Additionally, cpu topology information is provided under
  36 /sys/devices/system/cpu and includes these files.  The internal
  37 source for the output is in brackets ("[]").
  38
  39     kernel_max: the maximum cpu index allowed by the kernel configuration.
  40                 [NR_CPUS-1]
  41
  42     offline:    cpus that are not online because they have been
  43                 HOTPLUGGED off (see cpu-hotplug.txt) or exceed the limit
  44                 of cpus allowed by the kernel configuration (kernel_max
  45                 above). [~cpu_online_mask + cpus >= NR_CPUS]
  46
  47     online:     cpus that are online and being scheduled [cpu_online_mask]
  48
  49     possible:   cpus that have been allocated resources and can be
  50                 brought online if they are present. [cpu_possible_mask]
  51
  52     present:    cpus that have been identified as being present in the
  53                 system. [cpu_present_mask]
  54
  55 The format for the above output is compatible with cpulist_parse()
  56 [see <linux/cpumask.h>].  Some examples follow.
  57
  58 In this example, there are 64 cpus in the system but cpus 32-63 exceed
  59 the kernel max which is limited to 0..31 by the NR_CPUS config option
  60 being 32.  Note also that cpus 2 and 4-31 are not online but could be
  61 brought online as they are both present and possible.
  62
  63      kernel_max: 31
  64         offline: 2,4-31,32-63
  65          online: 0-1,3
  66        possible: 0-31
  67         present: 0-31
  68
  69 In this example, the NR_CPUS config option is 128, but the kernel was
  70 started with possible_cpus=144.  There are 4 cpus in the system and cpu2
  71 was manually taken offline (and is the only cpu that can be brought
  72 online.)
  73
  74      kernel_max: 127
  75         offline: 2,4-127,128-143
  76          online: 0-1,3
  77        possible: 0-127
  78         present: 0-3
  79
  80 See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter
  81 as well as more information on the various cpumask's.