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Documentation / cputopology.txt




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Based on kernel version 2.6.34. Page generated on 2010-05-31 16:02 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/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.
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