ASR_BASE
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+===========================================
+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. They reside in
+/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.
+
+die_id:
+
+ the CPU die ID of cpuX. Typically it is the hardware platform's
+ identifier (rather than the kernel's). The actual value is
+ architecture and platform dependent.
+
+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.
+
+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.
+
+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.
+
+core_cpus:
+
+ internal kernel map of CPUs within the same core.
+ (deprecated name: "thread_siblings")
+
+core_cpus_list:
+
+ human-readable list of CPUs within the same core.
+ (deprecated name: "thread_siblings_list");
+
+package_cpus:
+
+ internal kernel map of the CPUs sharing the same physical_package_id.
+ (deprecated name: "core_siblings")
+
+package_cpus_list:
+
+ human-readable list of CPUs sharing the same physical_package_id.
+ (deprecated name: "core_siblings_list")
+
+die_cpus:
+
+ internal kernel map of CPUs within the same die.
+
+die_cpus_list:
+
+ human-readable list of CPUs within the same die.
+
+book_siblings:
+
+ internal kernel map of cpuX's hardware threads within the same
+ book_id.
+
+book_siblings_list:
+
+ human-readable list of cpuX's hardware threads within the same
+ book_id.
+
+drawer_siblings:
+
+ internal kernel map of cpuX's hardware threads within the same
+ drawer_id.
+
+drawer_siblings_list:
+
+ human-readable list of cpuX's hardware threads within the same
+ drawer_id.
+
+Architecture-neutral, drivers/base/topology.c, exports these attributes.
+However, the book and drawer related sysfs files will only be created if
+CONFIG_SCHED_BOOK and CONFIG_SCHED_DRAWER are selected, respectively.
+
+CONFIG_SCHED_BOOK and CONFIG_SCHED_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_die_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_die_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) topology_physical_package_id: -1
+2) topology_die_id: -1
+3) topology_core_id: 0
+4) topology_sibling_cpumask: just the given CPU
+5) topology_core_cpumask: just the given CPU
+6) topology_die_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.