What:		/sys/devices/system/cpu/
Date:		pre-git history
Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description:
		A collection of both global and individual CPU attributes

		Individual CPU attributes are contained in subdirectories
		named by the kernel's logical CPU number, e.g.:

		/sys/devices/system/cpu/cpu#/

What:		/sys/devices/system/cpu/kernel_max
		/sys/devices/system/cpu/offline
		/sys/devices/system/cpu/online
		/sys/devices/system/cpu/possible
		/sys/devices/system/cpu/present
Date:		December 2008
Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description:	CPU topology files that describe kernel limits related to
		hotplug. Briefly:

		kernel_max: the maximum cpu index allowed by the kernel
		configuration.

		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).

		online: cpus that are online and being scheduled.

		possible: cpus that have been allocated resources and can be
		brought online if they are present.

		present: cpus that have been identified as being present in
		the system.

		See Documentation/cputopology.txt for more information.


What:		/sys/devices/system/cpu/probe
		/sys/devices/system/cpu/release
Date:		November 2009
Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description:	Dynamic addition and removal of CPU's.  This is not hotplug
		removal, this is meant complete removal/addition of the CPU
		from the system.

		probe: writes to this file will dynamically add a CPU to the
		system.  Information written to the file to add CPU's is
		architecture specific.

		release: writes to this file dynamically remove a CPU from
		the system.  Information writtento the file to remove CPU's
		is architecture specific.

What:		/sys/devices/system/cpu/cpu#/node
Date:		October 2009
Contact:	Linux memory management mailing list <linux-mm@kvack.org>
Description:	Discover NUMA node a CPU belongs to

		When CONFIG_NUMA is enabled, a symbolic link that points
		to the corresponding NUMA node directory.

		For example, the following symlink is created for cpu42
		in NUMA node 2:

		/sys/devices/system/cpu/cpu42/node2 -> ../../node/node2


What:		/sys/devices/system/cpu/cpu#/topology/core_id
		/sys/devices/system/cpu/cpu#/topology/core_siblings
		/sys/devices/system/cpu/cpu#/topology/core_siblings_list
		/sys/devices/system/cpu/cpu#/topology/physical_package_id
		/sys/devices/system/cpu/cpu#/topology/thread_siblings
		/sys/devices/system/cpu/cpu#/topology/thread_siblings_list
Date:		December 2008
Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description:	CPU topology files that describe a logical CPU's relationship
		to other cores and threads in the same physical package.

		One cpu# directory is created per logical CPU in the system,
		e.g. /sys/devices/system/cpu/cpu42/.

		Briefly, the files above are:

		core_id: the CPU core ID of cpu#. Typically it is the
		hardware platform's identifier (rather than the kernel's).
		The actual value is architecture and platform dependent.

		core_siblings: internal kernel map of cpu#'s hardware threads
		within the same physical_package_id.

		core_siblings_list: human-readable list of the logical CPU
		numbers within the same physical_package_id as cpu#.

		physical_package_id: physical package id of cpu#. Typically
		corresponds to a physical socket number, but the actual value
		is architecture and platform dependent.

		thread_siblings: internel kernel map of cpu#'s hardware
		threads within the same core as cpu#

		thread_siblings_list: human-readable list of cpu#'s hardware
		threads within the same core as cpu#

		See Documentation/cputopology.txt for more information.


What:		/sys/devices/system/cpu/cpuidle/current_driver
		/sys/devices/system/cpu/cpuidle/current_governer_ro
Date:		September 2007
Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description:	Discover cpuidle policy and mechanism

		Various CPUs today support multiple idle levels that are
		differentiated by varying exit latencies and power
		consumption during idle.

		Idle policy (governor) is differentiated from idle mechanism
		(driver)

		current_driver: displays current idle mechanism

		current_governor_ro: displays current idle policy

		See files in Documentation/cpuidle/ for more information.


What:		/sys/devices/system/cpu/cpu#/cpufreq/*
Date:		pre-git history
Contact:	linux-pm@vger.kernel.org
Description:	Discover and change clock speed of CPUs

		Clock scaling allows you to change the clock speed of the
		CPUs on the fly. This is a nice method to save battery
		power, because the lower the clock speed, the less power
		the CPU consumes.

		There are many knobs to tweak in this directory.

		See files in Documentation/cpu-freq/ for more information.

		In particular, read Documentation/cpu-freq/user-guide.txt
		to learn how to control the knobs.


What:		/sys/devices/system/cpu/cpu#/cpufreq/freqdomain_cpus
Date:		June 2013
Contact:	linux-pm@vger.kernel.org
Description:	Discover CPUs in the same CPU frequency coordination domain

		freqdomain_cpus is the list of CPUs (online+offline) that share
		the same clock/freq domain (possibly at the hardware level).
		That information may be hidden from the cpufreq core and the
		value of related_cpus may be different from freqdomain_cpus. This
		attribute is useful for user space DVFS controllers to get better
		power/performance results for platforms using acpi-cpufreq.

		This file is only present if the acpi-cpufreq driver is in use.


What:		/sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
Date:		August 2008
KernelVersion:	2.6.27
Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description:	Disable L3 cache indices

		These files exist in every CPU's cache/index3 directory. Each
		cache_disable_{0,1} file corresponds to one disable slot which
		can be used to disable a cache index. Reading from these files
		on a processor with this functionality will return the currently
		disabled index for that node. There is one L3 structure per
		node, or per internal node on MCM machines. Writing a valid
		index to one of these files will cause the specificed cache
		index to be disabled.

		All AMD processors with L3 caches provide this functionality.
		For details, see BKDGs at
		http://developer.amd.com/documentation/guides/Pages/default.aspx


What:		/sys/devices/system/cpu/cpufreq/boost
Date:		August 2012
Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description:	Processor frequency boosting control

		This switch controls the boost setting for the whole system.
		Boosting allows the CPU and the firmware to run at a frequency
		beyound it's nominal limit.
		More details can be found in Documentation/cpu-freq/boost.txt


What:		/sys/devices/system/cpu/cpu#/crash_notes
		/sys/devices/system/cpu/cpu#/crash_notes_size
Date:		April 2013
Contact:	kexec@lists.infradead.org
Description:	address and size of the percpu note.

		crash_notes: the physical address of the memory that holds the
		note of cpu#.

		crash_notes_size: size of the note of cpu#.


What:		/sys/devices/system/cpu/intel_pstate/max_perf_pct
		/sys/devices/system/cpu/intel_pstate/min_perf_pct
		/sys/devices/system/cpu/intel_pstate/no_turbo
Date:		February 2013
Contact:	linux-pm@vger.kernel.org
Description:	Parameters for the Intel P-state driver

		Logic for selecting the current P-state in Intel
		Sandybridge+ processors. The three knobs control
		limits for the P-state that will be requested by the
		driver.

		max_perf_pct: limits the maximum P state that will be requested by
		the driver stated as a percentage of the available performance.

		min_perf_pct: limits the minimum P state that will be requested by
		the driver stated as a percentage of the available performance.

		no_turbo: limits the driver to selecting P states below the turbo
		frequency range.

		More details can be found in Documentation/cpu-freq/intel-pstate.txt

What:		/sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below>
Date:		July 2014(documented, existed before August 2008)
Contact:	Sudeep Holla <sudeep.holla@arm.com>
		Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description:	Parameters for the CPU cache attributes

		allocation_policy:
			- WriteAllocate: allocate a memory location to a cache line
					 on a cache miss because of a write
			- ReadAllocate: allocate a memory location to a cache line
					on a cache miss because of a read
			- ReadWriteAllocate: both writeallocate and readallocate

		attributes: LEGACY used only on IA64 and is same as write_policy

		coherency_line_size: the minimum amount of data in bytes that gets
				     transferred from memory to cache

		level: the cache hierarchy in the multi-level cache configuration

		number_of_sets: total number of sets in the cache, a set is a
				collection of cache lines with the same cache index

		physical_line_partition: number of physical cache line per cache tag

		shared_cpu_list: the list of logical cpus sharing the cache

		shared_cpu_map: logical cpu mask containing the list of cpus sharing
				the cache

		size: the total cache size in kB

		type:
			- Instruction: cache that only holds instructions
			- Data: cache that only caches data
			- Unified: cache that holds both data and instructions

		ways_of_associativity: degree of freedom in placing a particular block
					of memory in the cache

		write_policy:
			- WriteThrough: data is written to both the cache line
					and to the block in the lower-level memory
			- WriteBack: data is written only to the cache line and
				     the modified cache line is written to main
				     memory only when it is replaced

What:		/sys/devices/system/cpu/vulnerabilities
		/sys/devices/system/cpu/vulnerabilities/meltdown
		/sys/devices/system/cpu/vulnerabilities/spectre_v1
		/sys/devices/system/cpu/vulnerabilities/spectre_v2
		/sys/devices/system/cpu/vulnerabilities/spec_store_bypass
Date:		January 2018
Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description:	Information about CPU vulnerabilities

		The files are named after the code names of CPU
		vulnerabilities. The output of those files reflects the
		state of the CPUs in the system. Possible output values:

		"Not affected"	  CPU is not affected by the vulnerability
		"Vulnerable"	  CPU is affected and no mitigation in effect
		"Mitigation: $M"  CPU is affected and mitigation $M is in effect
