1
  2Export CPU topology info via sysfs. Items (attributes) are similar
  3to /proc/cpuinfo output of some architectures:
  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/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
 295) /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
 346) /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
 397) /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
 448) /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
 499) /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
 5410) /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
 5911) /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
 6412) /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
 69To implement it in an architecture-neutral way, a new source file,
 70drivers/base/topology.c, is to export the 6 to 12 attributes. The book
 71and drawer related sysfs files will only be created if CONFIG_SCHED_BOOK
 72and CONFIG_SCHED_DRAWER are selected.
 73
 74CONFIG_SCHED_BOOK and CONFIG_DRAWER are currently only used on s390, where
 75they reflect the cpu and cache hierarchy.
 76
 77For an architecture to support this feature, it must define some of
 78these 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
 88The type of **_id macros is int.
 89The type of **_cpumask macros is (const) struct cpumask *. The latter
 90correspond with appropriate **_siblings sysfs attributes (except for
 91topology_sibling_cpumask() which corresponds with thread_siblings).
 92
 93To be consistent on all architectures, include/linux/topology.h
 94provides default definitions for any of the above macros that are
 95not defined by include/asm-XXX/topology.h:
 961) physical_package_id: -1
 972) core_id: 0
 983) sibling_cpumask: just the given CPU
 994) core_cpumask: just the given CPU
100
101For architectures that don't support books (CONFIG_SCHED_BOOK) there are no
102default definitions for topology_book_id() and topology_book_cpumask().
103For architectures that don't support drawes (CONFIG_SCHED_DRAWER) there are
104no default definitions for topology_drawer_id() and topology_drawer_cpumask().
105
106Additionally, CPU topology information is provided under
107/sys/devices/system/cpu and includes these files.  The internal
108source 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
126The format for the above output is compatible with cpulist_parse()
127[see <linux/cpumask.h>].  Some examples follow.
128
129In this example, there are 64 CPUs in the system but cpus 32-63 exceed
130the kernel max which is limited to 0..31 by the NR_CPUS config option
131being 32.  Note also that CPUs 2 and 4-31 are not online but could be
132brought 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
140In this example, the NR_CPUS config option is 128, but the kernel was
141started with possible_cpus=144.  There are 4 CPUs in the system and cpu2
142was manually taken offline (and is the only CPU that can be brought
143online.)
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
151See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter
152as well as more information on the various cpumasks.