LXR linux/Documentation/cputopology.txt

   1
   2Export CPU topology info via sysfs. Items (attributes) are similar
   3to /proc/cpuinfo.
   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/thread_siblings:
  18
  19        internel kernel map of cpuX's hardware threads within the same
  20        core as cpuX
  21
  224) /sys/devices/system/cpu/cpuX/topology/core_siblings:
  23
  24        internal kernel map of cpuX's hardware threads within the same
  25        physical_package_id.
  26
  27To implement it in an architecture-neutral way, a new source file,
  28drivers/base/topology.c, is to export the 4 attributes.
  29
  30For an architecture to support this feature, it must define some of
  31these macros in include/asm-XXX/topology.h:
  32#define topology_physical_package_id(cpu)
  33#define topology_core_id(cpu)
  34#define topology_thread_cpumask(cpu)
  35#define topology_core_cpumask(cpu)
  36
  37The type of **_id is int.
  38The type of siblings is (const) struct cpumask *.
  39
  40To be consistent on all architectures, include/linux/topology.h
  41provides default definitions for any of the above macros that are
  42not defined by include/asm-XXX/topology.h:
  431) physical_package_id: -1
  442) core_id: 0
  453) thread_siblings: just the given CPU
  464) core_siblings: just the given CPU
  47
  48Additionally, CPU topology information is provided under
  49/sys/devices/system/cpu and includes these files.  The internal
  50source for the output is in brackets ("[]").
  51
  52    kernel_max: the maximum CPU index allowed by the kernel configuration.
  53                [NR_CPUS-1]
  54
  55    offline:    CPUs that are not online because they have been
  56                HOTPLUGGED off (see cpu-hotplug.txt) or exceed the limit
  57                of CPUs allowed by the kernel configuration (kernel_max
  58                above). [~cpu_online_mask + cpus >= NR_CPUS]
  59
  60    online:     CPUs that are online and being scheduled [cpu_online_mask]
  61
  62    possible:   CPUs that have been allocated resources and can be
  63                brought online if they are present. [cpu_possible_mask]
  64
  65    present:    CPUs that have been identified as being present in the
  66                system. [cpu_present_mask]
  67
  68The format for the above output is compatible with cpulist_parse()
  69[see <linux/cpumask.h>].  Some examples follow.
  70
  71In this example, there are 64 CPUs in the system but cpus 32-63 exceed
  72the kernel max which is limited to 0..31 by the NR_CPUS config option
  73being 32.  Note also that CPUs 2 and 4-31 are not online but could be
  74brought online as they are both present and possible.
  75
  76     kernel_max: 31
  77        offline: 2,4-31,32-63
  78         online: 0-1,3
  79       possible: 0-31
  80        present: 0-31
  81
  82In this example, the NR_CPUS config option is 128, but the kernel was
  83started with possible_cpus=144.  There are 4 CPUs in the system and cpu2
  84was manually taken offline (and is the only CPU that can be brought
  85online.)
  86
  87     kernel_max: 127
  88        offline: 2,4-127,128-143
  89         online: 0-1,3
  90       possible: 0-127
  91        present: 0-3
  92
  93See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter
  94as well as more information on the various cpumasks.
  95