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Documentation / cputopology.txt




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Based on kernel version 3.2. Page generated on 2012-01-05 23:28 EST.

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.
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