Documentation/admin-guide/cputopology.rst

Source file repositories/reference/linux-study-clean/Documentation/admin-guide/cputopology.rst

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Linux kernel
Corpus path
Documentation/admin-guide/cputopology.rst
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.rst
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3932 bytes
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102
Domain
Support Tooling And Documentation
Bucket
Documentation
Inferred role
Support Tooling And Documentation: documentation
Status
atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

===========================================
How CPU topology info is exported via sysfs
===========================================

CPU topology info is exported via sysfs. Items (attributes) are similar
to /proc/cpuinfo output of some architectures. They reside in
/sys/devices/system/cpu/cpuX/topology/. Please refer to the ABI file:
Documentation/ABI/stable/sysfs-devices-system-cpu.

Architecture-neutral, drivers/base/topology.c, exports these attributes.
However the die, cluster, book, and drawer hierarchy related sysfs files will
only be created if an architecture provides the related macros as described
below.

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_cluster_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_cluster_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_cluster_id: -1
4) topology_core_id: 0
5) topology_book_id: -1
6) topology_drawer_id: -1
7) topology_sibling_cpumask: just the given CPU
8) topology_core_cpumask: just the given CPU
9) topology_cluster_cpumask: just the given CPU
10) topology_die_cpumask: just the given CPU
11) topology_book_cpumask:  just the given CPU
12) topology_drawer_cpumask: just the given CPU

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 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]

Annotation

Implementation Notes