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-
-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.