1 ===========================================
2 How CPU topology info is exported via sysfs
3 ===========================================
4
5 CPU topology info is exported via sysfs. Items
6 to /proc/cpuinfo output of some architectures.
7 /sys/devices/system/cpu/cpuX/topology/. Please
8 Documentation/ABI/stable/sysfs-devices-system-
9
10 Architecture-neutral, drivers/base/topology.c,
11 However the die, cluster, book, and drawer hie
12 only be created if an architecture provides th
13 below.
14
15 For an architecture to support this feature, i
16 these macros in include/asm-XXX/topology.h::
17
18 #define topology_physical_package_id(c
19 #define topology_die_id(cpu)
20 #define topology_cluster_id(cpu)
21 #define topology_core_id(cpu)
22 #define topology_book_id(cpu)
23 #define topology_drawer_id(cpu)
24 #define topology_sibling_cpumask(cpu)
25 #define topology_core_cpumask(cpu)
26 #define topology_cluster_cpumask(cpu)
27 #define topology_die_cpumask(cpu)
28 #define topology_book_cpumask(cpu)
29 #define topology_drawer_cpumask(cpu)
30
31 The type of ``**_id macros`` is int.
32 The type of ``**_cpumask macros`` is ``(const)
33 correspond with appropriate ``**_siblings`` sy
34 topology_sibling_cpumask() which corresponds w
35
36 To be consistent on all architectures, include
37 provides default definitions for any of the ab
38 not defined by include/asm-XXX/topology.h:
39
40 1) topology_physical_package_id: -1
41 2) topology_die_id: -1
42 3) topology_cluster_id: -1
43 4) topology_core_id: 0
44 5) topology_book_id: -1
45 6) topology_drawer_id: -1
46 7) topology_sibling_cpumask: just the given CP
47 8) topology_core_cpumask: just the given CPU
48 9) topology_cluster_cpumask: just the given CP
49 10) topology_die_cpumask: just the given CPU
50 11) topology_book_cpumask: just the given CPU
51 12) topology_drawer_cpumask: just the given CP
52
53 Additionally, CPU topology information is prov
54 /sys/devices/system/cpu and includes these fil
55 source for the output is in brackets ("[]").
56
57 =========== ==============================
58 kernel_max: the maximum CPU index allowed
59 [NR_CPUS-1]
60
61 offline: CPUs that are not online becau
62 HOTPLUGGED off or exceed the l
63 kernel configuration (kernel_m
64 [~cpu_online_mask + cpus >= NR
65
66 online: CPUs that are online and being
67
68 possible: CPUs that have been allocated
69 brought online if they are pre
70
71 present: CPUs that have been identified
72 system. [cpu_present_mask]
73 =========== ==============================
74
75 The format for the above output is compatible
76 [see <linux/cpumask.h>]. Some examples follow
77
78 In this example, there are 64 CPUs in the syst
79 the kernel max which is limited to 0..31 by th
80 being 32. Note also that CPUs 2 and 4-31 are
81 brought online as they are both present and po
82
83 kernel_max: 31
84 offline: 2,4-31,32-63
85 online: 0-1,3
86 possible: 0-31
87 present: 0-31
88
89 In this example, the NR_CPUS config option is
90 started with possible_cpus=144. There are 4 C
91 was manually taken offline (and is the only CP
92 online.)::
93
94 kernel_max: 127
95 offline: 2,4-127,128-143
96 online: 0-1,3
97 possible: 0-127
98 present: 0-3
99
100 See Documentation/core-api/cpu_hotplug.rst for
101 kernel start parameter as well as more informa
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