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/thread_siblings: internal kernel map of cpuX's hardware threads within the same core as cpuX. 5) /sys/devices/system/cpu/cpuX/topology/thread_siblings_list: human-readable list of cpuX's hardware threads within the same core as cpuX. 6) /sys/devices/system/cpu/cpuX/topology/core_siblings: internal kernel map of cpuX's hardware threads within the same physical_package_id. 7) /sys/devices/system/cpu/cpuX/topology/core_siblings_list: human-readable list of cpuX's hardware threads within the same physical_package_id. 8) /sys/devices/system/cpu/cpuX/topology/book_siblings: internal kernel map of cpuX's hardware threads within the same book_id. 9) /sys/devices/system/cpu/cpuX/topology/book_siblings_list: human-readable list 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 6 or 9 attributes. The three 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_sibling_cpumask(cpu) #define topology_core_cpumask(cpu) #define topology_book_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(). 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.