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Diffstat (limited to 'Documentation/cputopology.txt')
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diff --git a/Documentation/cputopology.txt b/Documentation/cputopology.txt new file mode 100644 index 00000000..902d3151 --- /dev/null +++ b/Documentation/cputopology.txt @@ -0,0 +1,111 @@ + +Export CPU topology info via sysfs. Items (attributes) are similar +to /proc/cpuinfo. + +1) /sys/devices/system/cpu/cpuX/topology/physical_package_id: + + physical package id of cpuX. Typically corresponds to a physical + socket number, but the actual value is architecture and platform + dependent. + +2) /sys/devices/system/cpu/cpuX/topology/core_id: + + the CPU core ID of cpuX. Typically it is the hardware platform's + identifier (rather than the kernel's). The actual value is + architecture and platform dependent. + +3) /sys/devices/system/cpu/cpuX/topology/book_id: + + the book ID of cpuX. Typically it is the hardware platform's + identifier (rather than the kernel's). The actual value is + architecture and platform dependent. + +4) /sys/devices/system/cpu/cpuX/topology/thread_siblings: + + internel kernel map of cpuX's hardware threads within the same + core as cpuX + +5) /sys/devices/system/cpu/cpuX/topology/core_siblings: + + internal kernel map of cpuX's hardware threads within the same + physical_package_id. + +6) /sys/devices/system/cpu/cpuX/topology/book_siblings: + + internal kernel map of cpuX's hardware threads within the same + book_id. + +To implement it in an architecture-neutral way, a new source file, +drivers/base/topology.c, is to export the 4 or 6 attributes. The two book +related sysfs files will only be created if CONFIG_SCHED_BOOK is selected. + +For an architecture to support this feature, it must define some of +these macros in include/asm-XXX/topology.h: +#define topology_physical_package_id(cpu) +#define topology_core_id(cpu) +#define topology_book_id(cpu) +#define topology_thread_cpumask(cpu) +#define topology_core_cpumask(cpu) +#define topology_book_cpumask(cpu) + +The type of **_id is int. +The type of siblings is (const) struct cpumask *. + +To be consistent on all architectures, include/linux/topology.h +provides default definitions for any of the above macros that are +not defined by include/asm-XXX/topology.h: +1) physical_package_id: -1 +2) core_id: 0 +3) thread_siblings: just the given CPU +4) core_siblings: just the given CPU + +For architectures that don't support books (CONFIG_SCHED_BOOK) there are no +default definitions for topology_book_id() and topology_book_cpumask(). + +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 cpumasks. |