d62720ade8
Add information to cputopology.txt explaining the output of various system cpumask's. Signed-off-by: Mike Travis <travis@sgi.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
81 lines
2.9 KiB
Text
81 lines
2.9 KiB
Text
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Export cpu topology info via sysfs. Items (attributes) are similar
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to /proc/cpuinfo.
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1) /sys/devices/system/cpu/cpuX/topology/physical_package_id:
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represent the physical package id of cpu X;
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2) /sys/devices/system/cpu/cpuX/topology/core_id:
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represent the cpu core id to cpu X;
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3) /sys/devices/system/cpu/cpuX/topology/thread_siblings:
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represent the thread siblings to cpu X in the same core;
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4) /sys/devices/system/cpu/cpuX/topology/core_siblings:
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represent the thread siblings to cpu X in the same physical package;
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To implement it in an architecture-neutral way, a new source file,
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drivers/base/topology.c, is to export the 4 attributes.
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For an architecture to support this feature, it must define some of
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these macros in include/asm-XXX/topology.h:
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#define topology_physical_package_id(cpu)
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#define topology_core_id(cpu)
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#define topology_thread_siblings(cpu)
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#define topology_core_siblings(cpu)
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The type of **_id is int.
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The type of siblings is cpumask_t.
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To be consistent on all architectures, include/linux/topology.h
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provides default definitions for any of the above macros that are
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not defined by include/asm-XXX/topology.h:
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1) physical_package_id: -1
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2) core_id: 0
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3) thread_siblings: just the given CPU
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4) core_siblings: just the given CPU
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Additionally, cpu topology information is provided under
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/sys/devices/system/cpu and includes these files. The internal
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source for the output is in brackets ("[]").
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kernel_max: the maximum cpu index allowed by the kernel configuration.
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[NR_CPUS-1]
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offline: cpus that are not online because they have been
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HOTPLUGGED off (see cpu-hotplug.txt) or exceed the limit
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of cpus allowed by the kernel configuration (kernel_max
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above). [~cpu_online_mask + cpus >= NR_CPUS]
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online: cpus that are online and being scheduled [cpu_online_mask]
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possible: cpus that have been allocated resources and can be
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brought online if they are present. [cpu_possible_mask]
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present: cpus that have been identified as being present in the
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system. [cpu_present_mask]
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The format for the above output is compatible with cpulist_parse()
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[see <linux/cpumask.h>]. Some examples follow.
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In this example, there are 64 cpus in the system but cpus 32-63 exceed
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the kernel max which is limited to 0..31 by the NR_CPUS config option
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being 32. Note also that cpus 2 and 4-31 are not online but could be
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brought online as they are both present and possible.
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kernel_max: 31
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offline: 2,4-31,32-63
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online: 0-1,3
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possible: 0-31
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present: 0-31
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In this example, the NR_CPUS config option is 128, but the kernel was
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started with possible_cpus=144. There are 4 cpus in the system and cpu2
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was manually taken offline (and is the only cpu that can be brought
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online.)
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kernel_max: 127
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offline: 2,4-127,128-143
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online: 0-1,3
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possible: 0-127
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present: 0-3
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See cpu-hotplug.txt for the possible_cpus=NUM kernel start parameter
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as well as more information on the various cpumask's.
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