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Commit d62720ad authored by Mike Travis's avatar Mike Travis Committed by Rusty Russell
Browse files

sysfs: add documentation to cputopology.txt for system cpumasks 



Add information to cputopology.txt explaining the output of various
system cpumask's.

Signed-off-by: default avatarMike Travis <travis@sgi.com>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent e057d7ae

Documentation/cputopology.txt

+48 −0
Original line number Diff line number Diff line
@@ -31,3 +31,51 @@ not defined by include/asm-XXX/topology.h: 
2) core_id: 0

3) thread_siblings: just the given CPU

4) core_siblings: just the given CPU



Additionally, cpu topology information is provided under

/sys/devices/system/cpu and includes these files.  The internal

source for the output is in brackets ("[]").



    kernel_max: the maximum cpu index allowed by the kernel configuration.

		[NR_CPUS-1]



    offline:	cpus that are not online because they have been

		HOTPLUGGED off (see cpu-hotplug.txt) or exceed the limit

		of cpus allowed by the kernel configuration (kernel_max

		above). [~cpu_online_mask + cpus >= NR_CPUS]



    online:	cpus that are online and being scheduled [cpu_online_mask]



    possible:	cpus that have been allocated resources and can be

		brought online if they are present. [cpu_possible_mask]



    present:	cpus that have been identified as being present in the

		system. [cpu_present_mask]



The format for the above output is compatible with cpulist_parse()

[see <linux/cpumask.h>].  Some examples follow.



In this example, there are 64 cpus in the system but cpus 32-63 exceed

the kernel max which is limited to 0..31 by the NR_CPUS config option

being 32.  Note also that cpus 2 and 4-31 are not online but could be

brought online as they are both present and possible.



     kernel_max: 31

        offline: 2,4-31,32-63

         online: 0-1,3

       possible: 0-31

        present: 0-31



In this example, the NR_CPUS config option is 128, but the kernel was

started with possible_cpus=144.  There are 4 cpus in the system and cpu2

was manually taken offline (and is the only cpu that can be brought

online.)



     kernel_max: 127

        offline: 2,4-127,128-143

         online: 0-1,3

       possible: 0-127

        present: 0-3



See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter

as well as more information on the various cpumask's.