About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / cputopology.txt




Custom Search

Based on kernel version 3.15.4. Page generated on 2014-07-07 09:00 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		internal 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.
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.