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Documentation / cputopology.txt




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Based on kernel version 4.13.3. Page generated on 2017-09-23 13:54 EST.

1	===========================================
2	How CPU topology info is exported via sysfs
3	===========================================
4	
5	Export CPU topology info via sysfs. Items (attributes) are similar
6	to /proc/cpuinfo output of some architectures:
7	
8	1) /sys/devices/system/cpu/cpuX/topology/physical_package_id:
9	
10		physical package id of cpuX. Typically corresponds to a physical
11		socket number, but the actual value is architecture and platform
12		dependent.
13	
14	2) /sys/devices/system/cpu/cpuX/topology/core_id:
15	
16		the CPU core ID of cpuX. Typically it is the hardware platform's
17		identifier (rather than the kernel's).  The actual value is
18		architecture and platform dependent.
19	
20	3) /sys/devices/system/cpu/cpuX/topology/book_id:
21	
22		the book ID of cpuX. Typically it is the hardware platform's
23		identifier (rather than the kernel's).	The actual value is
24		architecture and platform dependent.
25	
26	4) /sys/devices/system/cpu/cpuX/topology/drawer_id:
27	
28		the drawer ID of cpuX. Typically it is the hardware platform's
29		identifier (rather than the kernel's).	The actual value is
30		architecture and platform dependent.
31	
32	5) /sys/devices/system/cpu/cpuX/topology/thread_siblings:
33	
34		internal kernel map of cpuX's hardware threads within the same
35		core as cpuX.
36	
37	6) /sys/devices/system/cpu/cpuX/topology/thread_siblings_list:
38	
39		human-readable list of cpuX's hardware threads within the same
40		core as cpuX.
41	
42	7) /sys/devices/system/cpu/cpuX/topology/core_siblings:
43	
44		internal kernel map of cpuX's hardware threads within the same
45		physical_package_id.
46	
47	8) /sys/devices/system/cpu/cpuX/topology/core_siblings_list:
48	
49		human-readable list of cpuX's hardware threads within the same
50		physical_package_id.
51	
52	9) /sys/devices/system/cpu/cpuX/topology/book_siblings:
53	
54		internal kernel map of cpuX's hardware threads within the same
55		book_id.
56	
57	10) /sys/devices/system/cpu/cpuX/topology/book_siblings_list:
58	
59		human-readable list of cpuX's hardware threads within the same
60		book_id.
61	
62	11) /sys/devices/system/cpu/cpuX/topology/drawer_siblings:
63	
64		internal kernel map of cpuX's hardware threads within the same
65		drawer_id.
66	
67	12) /sys/devices/system/cpu/cpuX/topology/drawer_siblings_list:
68	
69		human-readable list of cpuX's hardware threads within the same
70		drawer_id.
71	
72	To implement it in an architecture-neutral way, a new source file,
73	drivers/base/topology.c, is to export the 6 to 12 attributes. The book
74	and drawer related sysfs files will only be created if CONFIG_SCHED_BOOK
75	and CONFIG_SCHED_DRAWER are selected.
76	
77	CONFIG_SCHED_BOOK and CONFIG_DRAWER are currently only used on s390, where
78	they reflect the cpu and cache hierarchy.
79	
80	For an architecture to support this feature, it must define some of
81	these macros in include/asm-XXX/topology.h::
82	
83		#define topology_physical_package_id(cpu)
84		#define topology_core_id(cpu)
85		#define topology_book_id(cpu)
86		#define topology_drawer_id(cpu)
87		#define topology_sibling_cpumask(cpu)
88		#define topology_core_cpumask(cpu)
89		#define topology_book_cpumask(cpu)
90		#define topology_drawer_cpumask(cpu)
91	
92	The type of ``**_id macros`` is int.
93	The type of ``**_cpumask macros`` is ``(const) struct cpumask *``. The latter
94	correspond with appropriate ``**_siblings`` sysfs attributes (except for
95	topology_sibling_cpumask() which corresponds with thread_siblings).
96	
97	To be consistent on all architectures, include/linux/topology.h
98	provides default definitions for any of the above macros that are
99	not defined by include/asm-XXX/topology.h:
100	
101	1) physical_package_id: -1
102	2) core_id: 0
103	3) sibling_cpumask: just the given CPU
104	4) core_cpumask: just the given CPU
105	
106	For architectures that don't support books (CONFIG_SCHED_BOOK) there are no
107	default definitions for topology_book_id() and topology_book_cpumask().
108	For architectures that don't support drawers (CONFIG_SCHED_DRAWER) there are
109	no default definitions for topology_drawer_id() and topology_drawer_cpumask().
110	
111	Additionally, CPU topology information is provided under
112	/sys/devices/system/cpu and includes these files.  The internal
113	source for the output is in brackets ("[]").
114	
115	    =========== ==========================================================
116	    kernel_max: the maximum CPU index allowed by the kernel configuration.
117			[NR_CPUS-1]
118	
119	    offline:	CPUs that are not online because they have been
120			HOTPLUGGED off (see cpu-hotplug.txt) or exceed the limit
121			of CPUs allowed by the kernel configuration (kernel_max
122			above). [~cpu_online_mask + cpus >= NR_CPUS]
123	
124	    online:	CPUs that are online and being scheduled [cpu_online_mask]
125	
126	    possible:	CPUs that have been allocated resources and can be
127			brought online if they are present. [cpu_possible_mask]
128	
129	    present:	CPUs that have been identified as being present in the
130			system. [cpu_present_mask]
131	    =========== ==========================================================
132	
133	The format for the above output is compatible with cpulist_parse()
134	[see <linux/cpumask.h>].  Some examples follow.
135	
136	In this example, there are 64 CPUs in the system but cpus 32-63 exceed
137	the kernel max which is limited to 0..31 by the NR_CPUS config option
138	being 32.  Note also that CPUs 2 and 4-31 are not online but could be
139	brought online as they are both present and possible::
140	
141	     kernel_max: 31
142	        offline: 2,4-31,32-63
143	         online: 0-1,3
144	       possible: 0-31
145	        present: 0-31
146	
147	In this example, the NR_CPUS config option is 128, but the kernel was
148	started with possible_cpus=144.  There are 4 CPUs in the system and cpu2
149	was manually taken offline (and is the only CPU that can be brought
150	online.)::
151	
152	     kernel_max: 127
153	        offline: 2,4-127,128-143
154	         online: 0-1,3
155	       possible: 0-127
156	        present: 0-3
157	
158	See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter
159	as well as more information on the various cpumasks.
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