Root/
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. |
95 |
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