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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/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 | |
23 | 4) /sys/devices/system/cpu/cpuX/topology/thread_siblings: |
24 | |
25 | internel kernel map of cpuX's hardware threads within the same |
26 | core as cpuX |
27 | |
28 | 5) /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 | |
33 | 6) /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 | |
38 | To implement it in an architecture-neutral way, a new source file, |
39 | drivers/base/topology.c, is to export the 4 or 6 attributes. The two book |
40 | related sysfs files will only be created if CONFIG_SCHED_BOOK is selected. |
41 | |
42 | For an architecture to support this feature, it must define some of |
43 | these 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 | |
51 | The type of **_id is int. |
52 | The type of siblings is (const) struct cpumask *. |
53 | |
54 | To be consistent on all architectures, include/linux/topology.h |
55 | provides default definitions for any of the above macros that are |
56 | not defined by include/asm-XXX/topology.h: |
57 | 1) physical_package_id: -1 |
58 | 2) core_id: 0 |
59 | 3) thread_siblings: just the given CPU |
60 | 4) core_siblings: just the given CPU |
61 | |
62 | For architectures that don't support books (CONFIG_SCHED_BOOK) there are no |
63 | default definitions for topology_book_id() and topology_book_cpumask(). |
64 | |
65 | Additionally, CPU topology information is provided under |
66 | /sys/devices/system/cpu and includes these files. The internal |
67 | source 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 | |
85 | The format for the above output is compatible with cpulist_parse() |
86 | [see <linux/cpumask.h>]. Some examples follow. |
87 | |
88 | In this example, there are 64 CPUs in the system but cpus 32-63 exceed |
89 | the kernel max which is limited to 0..31 by the NR_CPUS config option |
90 | being 32. Note also that CPUs 2 and 4-31 are not online but could be |
91 | brought 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 | |
99 | In this example, the NR_CPUS config option is 128, but the kernel was |
100 | started with possible_cpus=144. There are 4 CPUs in the system and cpu2 |
101 | was manually taken offline (and is the only CPU that can be brought |
102 | online.) |
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 | |
110 | See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter |
111 | as well as more information on the various cpumasks. |
112 |
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