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