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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 | ||
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 | ||
11 | 2) /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 | ||
17 | 3) /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 | ||
22 | 4) /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 | ||
27 | To implement it in an architecture-neutral way, a new source file, | |
28 | drivers/base/topology.c, is to export the 4 attributes. | |
29 | ||
30 | For an architecture to support this feature, it must define some of | |
31 | these 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 | ||
37 | The type of **_id is int. | |
38 | The type of siblings is (const) struct cpumask *. | |
39 | ||
40 | To be consistent on all architectures, include/linux/topology.h | |
41 | provides default definitions for any of the above macros that are | |
42 | not defined by include/asm-XXX/topology.h: | |
43 | 1) physical_package_id: -1 | |
44 | 2) core_id: 0 | |
45 | 3) thread_siblings: just the given CPU | |
46 | 4) core_siblings: just the given CPU | |
47 | ||
48 | Additionally, CPU topology information is provided under | |
49 | /sys/devices/system/cpu and includes these files. The internal | |
50 | source 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 | ||
68 | The format for the above output is compatible with cpulist_parse() | |
69 | [see <linux/cpumask.h>]. Some examples follow. | |
70 | ||
71 | In this example, there are 64 CPUs in the system but cpus 32-63 exceed | |
72 | the kernel max which is limited to 0..31 by the NR_CPUS config option | |
73 | being 32. Note also that CPUs 2 and 4-31 are not online but could be | |
74 | brought 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 | ||
82 | In this example, the NR_CPUS config option is 128, but the kernel was | |
83 | started with possible_cpus=144. There are 4 CPUs in the system and cpu2 | |
84 | was manually taken offline (and is the only CPU that can be brought | |
85 | online.) | |
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 | ||
93 | See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter | |
94 | as well as more information on the various cpumasks. |