Kernel-3.10.0-957.el7_cputopology

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/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:

   internel kernel map 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/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_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 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().
For architectures that don’t support drawes (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.