tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
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linux
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.