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diff --git a/Documentation/cputopology.txt b/Documentation/cputopology.txt new file mode 100644 index 000000000..c6e7e9196 --- /dev/null +++ b/Documentation/cputopology.txt @@ -0,0 +1,159 @@ +=========================================== +How CPU topology info is exported via sysfs +=========================================== + +Export CPU topology info via sysfs. Items (attributes) are similar +to /proc/cpuinfo output of some architectures: + +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/drawer_id: + + the drawer ID of cpuX. Typically it is the hardware platform's + identifier (rather than the kernel's). The actual value is + architecture and platform dependent. + +5) /sys/devices/system/cpu/cpuX/topology/thread_siblings: + + internal kernel map of cpuX's hardware threads within the same + core as cpuX. + +6) /sys/devices/system/cpu/cpuX/topology/thread_siblings_list: + + human-readable list of cpuX's hardware threads within the same + core as cpuX. + +7) /sys/devices/system/cpu/cpuX/topology/core_siblings: + + internal kernel map of cpuX's hardware threads within the same + physical_package_id. + +8) /sys/devices/system/cpu/cpuX/topology/core_siblings_list: + + human-readable list of cpuX's hardware threads within the same + physical_package_id. + +9) /sys/devices/system/cpu/cpuX/topology/book_siblings: + + internal kernel map of cpuX's hardware threads within the same + book_id. + +10) /sys/devices/system/cpu/cpuX/topology/book_siblings_list: + + human-readable list of cpuX's hardware threads within the same + book_id. + +11) /sys/devices/system/cpu/cpuX/topology/drawer_siblings: + + internal kernel map of cpuX's hardware threads within the same + drawer_id. + +12) /sys/devices/system/cpu/cpuX/topology/drawer_siblings_list: + + human-readable list of cpuX's hardware threads within the same + drawer_id. + +To implement it in an architecture-neutral way, a new source file, +drivers/base/topology.c, is to export the 6 to 12 attributes. The book +and drawer related sysfs files will only be created if CONFIG_SCHED_BOOK +and CONFIG_SCHED_DRAWER are selected. + +CONFIG_SCHED_BOOK and CONFIG_DRAWER are currently only used on s390, where +they reflect the cpu and cache hierarchy. + +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_drawer_id(cpu) + #define topology_sibling_cpumask(cpu) + #define topology_core_cpumask(cpu) + #define topology_book_cpumask(cpu) + #define topology_drawer_cpumask(cpu) + +The type of ``**_id macros`` is int. +The type of ``**_cpumask macros`` is ``(const) struct cpumask *``. The latter +correspond with appropriate ``**_siblings`` sysfs attributes (except for +topology_sibling_cpumask() which corresponds with thread_siblings). + +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) sibling_cpumask: just the given CPU +4) core_cpumask: 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(). +For architectures that don't support drawers (CONFIG_SCHED_DRAWER) there are +no default definitions for topology_drawer_id() and topology_drawer_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. |