1What:		/sys/devices/system/cpu/
2Date:		pre-git history
3Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
4Description:
5		A collection of both global and individual CPU attributes
6
7		Individual CPU attributes are contained in subdirectories
8		named by the kernel's logical CPU number, e.g.:
9
10		/sys/devices/system/cpu/cpu#/
11
12What:		/sys/devices/system/cpu/kernel_max
13		/sys/devices/system/cpu/offline
14		/sys/devices/system/cpu/online
15		/sys/devices/system/cpu/possible
16		/sys/devices/system/cpu/present
17Date:		December 2008
18Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
19Description:	CPU topology files that describe kernel limits related to
20		hotplug. Briefly:
21
22		kernel_max: the maximum cpu index allowed by the kernel
23		configuration.
24
25		offline: cpus that are not online because they have been
26		HOTPLUGGED off or exceed the limit of cpus allowed by the
27		kernel configuration (kernel_max above).
28
29		online: cpus that are online and being scheduled.
30
31		possible: cpus that have been allocated resources and can be
32		brought online if they are present.
33
34		present: cpus that have been identified as being present in
35		the system.
36
37		See Documentation/cputopology.txt for more information.
38
39
40What:		/sys/devices/system/cpu/probe
41		/sys/devices/system/cpu/release
42Date:		November 2009
43Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
44Description:	Dynamic addition and removal of CPU's.  This is not hotplug
45		removal, this is meant complete removal/addition of the CPU
46		from the system.
47
48		probe: writes to this file will dynamically add a CPU to the
49		system.  Information written to the file to add CPU's is
50		architecture specific.
51
52		release: writes to this file dynamically remove a CPU from
53		the system.  Information writtento the file to remove CPU's
54		is architecture specific.
55
56What:		/sys/devices/system/cpu/cpu#/node
57Date:		October 2009
58Contact:	Linux memory management mailing list <linux-mm@kvack.org>
59Description:	Discover NUMA node a CPU belongs to
60
61		When CONFIG_NUMA is enabled, a symbolic link that points
62		to the corresponding NUMA node directory.
63
64		For example, the following symlink is created for cpu42
65		in NUMA node 2:
66
67		/sys/devices/system/cpu/cpu42/node2 -> ../../node/node2
68
69
70What:		/sys/devices/system/cpu/cpu#/topology/core_id
71		/sys/devices/system/cpu/cpu#/topology/core_siblings
72		/sys/devices/system/cpu/cpu#/topology/core_siblings_list
73		/sys/devices/system/cpu/cpu#/topology/physical_package_id
74		/sys/devices/system/cpu/cpu#/topology/thread_siblings
75		/sys/devices/system/cpu/cpu#/topology/thread_siblings_list
76Date:		December 2008
77Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
78Description:	CPU topology files that describe a logical CPU's relationship
79		to other cores and threads in the same physical package.
80
81		One cpu# directory is created per logical CPU in the system,
82		e.g. /sys/devices/system/cpu/cpu42/.
83
84		Briefly, the files above are:
85
86		core_id: the CPU core ID of cpu#. Typically it is the
87		hardware platform's identifier (rather than the kernel's).
88		The actual value is architecture and platform dependent.
89
90		core_siblings: internal kernel map of cpu#'s hardware threads
91		within the same physical_package_id.
92
93		core_siblings_list: human-readable list of the logical CPU
94		numbers within the same physical_package_id as cpu#.
95
96		physical_package_id: physical package id of cpu#. Typically
97		corresponds to a physical socket number, but the actual value
98		is architecture and platform dependent.
99
100		thread_siblings: internel kernel map of cpu#'s hardware
101		threads within the same core as cpu#
102
103		thread_siblings_list: human-readable list of cpu#'s hardware
104		threads within the same core as cpu#
105
106		See Documentation/cputopology.txt for more information.
107
108
109What:		/sys/devices/system/cpu/cpuidle/current_driver
110		/sys/devices/system/cpu/cpuidle/current_governer_ro
111		/sys/devices/system/cpu/cpuidle/available_governors
112		/sys/devices/system/cpu/cpuidle/current_governor
113Date:		September 2007
114Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
115Description:	Discover cpuidle policy and mechanism
116
117		Various CPUs today support multiple idle levels that are
118		differentiated by varying exit latencies and power
119		consumption during idle.
120
121		Idle policy (governor) is differentiated from idle mechanism
122		(driver)
123
124		current_driver: (RO) displays current idle mechanism
125
126		current_governor_ro: (RO) displays current idle policy
127
128		With the cpuidle_sysfs_switch boot option enabled (meant for
129		developer testing), the following three attributes are visible
130		instead:
131
132		current_driver: same as described above
133
134		available_governors: (RO) displays a space separated list of
135		available governors
136
137		current_governor: (RW) displays current idle policy. Users can
138		switch the governor at runtime by writing to this file.
139
140		See files in Documentation/cpuidle/ for more information.
141
142
143What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/name
144		/sys/devices/system/cpu/cpuX/cpuidle/stateN/latency
145		/sys/devices/system/cpu/cpuX/cpuidle/stateN/power
146		/sys/devices/system/cpu/cpuX/cpuidle/stateN/time
147		/sys/devices/system/cpu/cpuX/cpuidle/stateN/usage
148		/sys/devices/system/cpu/cpuX/cpuidle/stateN/above
149		/sys/devices/system/cpu/cpuX/cpuidle/stateN/below
150Date:		September 2007
151KernelVersion:	v2.6.24
152Contact:	Linux power management list <linux-pm@vger.kernel.org>
153Description:
154		The directory /sys/devices/system/cpu/cpuX/cpuidle contains per
155		logical CPU specific cpuidle information for each online cpu X.
156		The processor idle states which are available for use have the
157		following attributes:
158
159		name: (RO) Name of the idle state (string).
160
161		latency: (RO) The latency to exit out of this idle state (in
162		microseconds).
163
164		power: (RO) The power consumed while in this idle state (in
165		milliwatts).
166
167		time: (RO) The total time spent in this idle state (in microseconds).
168
169		usage: (RO) Number of times this state was entered (a count).
170
171		above: (RO) Number of times this state was entered, but the
172		       observed CPU idle duration was too short for it (a count).
173
174		below: (RO) Number of times this state was entered, but the
175		       observed CPU idle duration was too long for it (a count).
176
177What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/desc
178Date:		February 2008
179KernelVersion:	v2.6.25
180Contact:	Linux power management list <linux-pm@vger.kernel.org>
181Description:
182		(RO) A small description about the idle state (string).
183
184
185What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/disable
186Date:		March 2012
187KernelVersion:	v3.10
188Contact:	Linux power management list <linux-pm@vger.kernel.org>
189Description:
190		(RW) Option to disable this idle state (bool). The behavior and
191		the effect of the disable variable depends on the implementation
192		of a particular governor. In the ladder governor, for example,
193		it is not coherent, i.e. if one is disabling a light state, then
194		all deeper states are disabled as well, but the disable variable
195		does not reflect it. Likewise, if one enables a deep state but a
196		lighter state still is disabled, then this has no effect.
197
198
199What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/residency
200Date:		March 2014
201KernelVersion:	v3.15
202Contact:	Linux power management list <linux-pm@vger.kernel.org>
203Description:
204		(RO) Display the target residency i.e. the minimum amount of
205		time (in microseconds) this cpu should spend in this idle state
206		to make the transition worth the effort.
207
208What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/s2idle/
209Date:		March 2018
210KernelVersion:	v4.17
211Contact:	Linux power management list <linux-pm@vger.kernel.org>
212Description:
213		Idle state usage statistics related to suspend-to-idle.
214
215		This attribute group is only present for states that can be
216		used in suspend-to-idle with suspended timekeeping.
217
218What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/s2idle/time
219Date:		March 2018
220KernelVersion:	v4.17
221Contact:	Linux power management list <linux-pm@vger.kernel.org>
222Description:
223		Total time spent by the CPU in suspend-to-idle (with scheduler
224		tick suspended) after requesting this state.
225
226What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/s2idle/usage
227Date:		March 2018
228KernelVersion:	v4.17
229Contact:	Linux power management list <linux-pm@vger.kernel.org>
230Description:
231		Total number of times this state has been requested by the CPU
232		while entering suspend-to-idle.
233
234What:		/sys/devices/system/cpu/cpu#/cpufreq/*
235Date:		pre-git history
236Contact:	linux-pm@vger.kernel.org
237Description:	Discover and change clock speed of CPUs
238
239		Clock scaling allows you to change the clock speed of the
240		CPUs on the fly. This is a nice method to save battery
241		power, because the lower the clock speed, the less power
242		the CPU consumes.
243
244		There are many knobs to tweak in this directory.
245
246		See files in Documentation/cpu-freq/ for more information.
247
248
249What:		/sys/devices/system/cpu/cpu#/cpufreq/freqdomain_cpus
250Date:		June 2013
251Contact:	linux-pm@vger.kernel.org
252Description:	Discover CPUs in the same CPU frequency coordination domain
253
254		freqdomain_cpus is the list of CPUs (online+offline) that share
255		the same clock/freq domain (possibly at the hardware level).
256		That information may be hidden from the cpufreq core and the
257		value of related_cpus may be different from freqdomain_cpus. This
258		attribute is useful for user space DVFS controllers to get better
259		power/performance results for platforms using acpi-cpufreq.
260
261		This file is only present if the acpi-cpufreq driver is in use.
262
263
264What:		/sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
265Date:		August 2008
266KernelVersion:	2.6.27
267Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
268Description:	Disable L3 cache indices
269
270		These files exist in every CPU's cache/index3 directory. Each
271		cache_disable_{0,1} file corresponds to one disable slot which
272		can be used to disable a cache index. Reading from these files
273		on a processor with this functionality will return the currently
274		disabled index for that node. There is one L3 structure per
275		node, or per internal node on MCM machines. Writing a valid
276		index to one of these files will cause the specificed cache
277		index to be disabled.
278
279		All AMD processors with L3 caches provide this functionality.
280		For details, see BKDGs at
281		http://developer.amd.com/documentation/guides/Pages/default.aspx
282
283
284What:		/sys/devices/system/cpu/cpufreq/boost
285Date:		August 2012
286Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
287Description:	Processor frequency boosting control
288
289		This switch controls the boost setting for the whole system.
290		Boosting allows the CPU and the firmware to run at a frequency
291		beyound it's nominal limit.
292		More details can be found in
293		Documentation/admin-guide/pm/cpufreq.rst
294
295
296What:		/sys/devices/system/cpu/cpu#/crash_notes
297		/sys/devices/system/cpu/cpu#/crash_notes_size
298Date:		April 2013
299Contact:	kexec@lists.infradead.org
300Description:	address and size of the percpu note.
301
302		crash_notes: the physical address of the memory that holds the
303		note of cpu#.
304
305		crash_notes_size: size of the note of cpu#.
306
307
308What:		/sys/devices/system/cpu/intel_pstate/max_perf_pct
309		/sys/devices/system/cpu/intel_pstate/min_perf_pct
310		/sys/devices/system/cpu/intel_pstate/no_turbo
311Date:		February 2013
312Contact:	linux-pm@vger.kernel.org
313Description:	Parameters for the Intel P-state driver
314
315		Logic for selecting the current P-state in Intel
316		Sandybridge+ processors. The three knobs control
317		limits for the P-state that will be requested by the
318		driver.
319
320		max_perf_pct: limits the maximum P state that will be requested by
321		the driver stated as a percentage of the available performance.
322
323		min_perf_pct: limits the minimum P state that will be requested by
324		the driver stated as a percentage of the available performance.
325
326		no_turbo: limits the driver to selecting P states below the turbo
327		frequency range.
328
329		More details can be found in
330		Documentation/admin-guide/pm/intel_pstate.rst
331
332What:		/sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below>
333Date:		July 2014(documented, existed before August 2008)
334Contact:	Sudeep Holla <sudeep.holla@arm.com>
335		Linux kernel mailing list <linux-kernel@vger.kernel.org>
336Description:	Parameters for the CPU cache attributes
337
338		allocation_policy:
339			- WriteAllocate: allocate a memory location to a cache line
340					 on a cache miss because of a write
341			- ReadAllocate: allocate a memory location to a cache line
342					on a cache miss because of a read
343			- ReadWriteAllocate: both writeallocate and readallocate
344
345		attributes: LEGACY used only on IA64 and is same as write_policy
346
347		coherency_line_size: the minimum amount of data in bytes that gets
348				     transferred from memory to cache
349
350		level: the cache hierarchy in the multi-level cache configuration
351
352		number_of_sets: total number of sets in the cache, a set is a
353				collection of cache lines with the same cache index
354
355		physical_line_partition: number of physical cache line per cache tag
356
357		shared_cpu_list: the list of logical cpus sharing the cache
358
359		shared_cpu_map: logical cpu mask containing the list of cpus sharing
360				the cache
361
362		size: the total cache size in kB
363
364		type:
365			- Instruction: cache that only holds instructions
366			- Data: cache that only caches data
367			- Unified: cache that holds both data and instructions
368
369		ways_of_associativity: degree of freedom in placing a particular block
370					of memory in the cache
371
372		write_policy:
373			- WriteThrough: data is written to both the cache line
374					and to the block in the lower-level memory
375			- WriteBack: data is written only to the cache line and
376				     the modified cache line is written to main
377				     memory only when it is replaced
378
379
380What:		/sys/devices/system/cpu/cpu*/cache/index*/id
381Date:		September 2016
382Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
383Description:	Cache id
384
385		The id provides a unique number for a specific instance of
386		a cache of a particular type. E.g. there may be a level
387		3 unified cache on each socket in a server and we may
388		assign them ids 0, 1, 2, ...
389
390		Note that id value can be non-contiguous. E.g. level 1
391		caches typically exist per core, but there may not be a
392		power of two cores on a socket, so these caches may be
393		numbered 0, 1, 2, 3, 4, 5, 8, 9, 10, ...
394
395What:		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats
396		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/turbo_stat
397		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/sub_turbo_stat
398		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/unthrottle
399		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/powercap
400		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overtemp
401		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/supply_fault
402		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overcurrent
403		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/occ_reset
404Date:		March 2016
405Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
406		Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
407Description:	POWERNV CPUFreq driver's frequency throttle stats directory and
408		attributes
409
410		'cpuX/cpufreq/throttle_stats' directory contains the CPU frequency
411		throttle stat attributes for the chip. The throttle stats of a cpu
412		is common across all the cpus belonging to a chip. Below are the
413		throttle attributes exported in the 'throttle_stats' directory:
414
415		- turbo_stat : This file gives the total number of times the max
416		frequency is throttled to lower frequency in turbo (at and above
417		nominal frequency) range of frequencies.
418
419		- sub_turbo_stat : This file gives the total number of times the
420		max frequency is throttled to lower frequency in sub-turbo(below
421		nominal frequency) range of frequencies.
422
423		- unthrottle : This file gives the total number of times the max
424		frequency is unthrottled after being throttled.
425
426		- powercap : This file gives the total number of times the max
427		frequency is throttled due to 'Power Capping'.
428
429		- overtemp : This file gives the total number of times the max
430		frequency is throttled due to 'CPU Over Temperature'.
431
432		- supply_fault : This file gives the total number of times the
433		max frequency is throttled due to 'Power Supply Failure'.
434
435		- overcurrent : This file gives the total number of times the
436		max frequency is throttled due to 'Overcurrent'.
437
438		- occ_reset : This file gives the total number of times the max
439		frequency is throttled due to 'OCC Reset'.
440
441		The sysfs attributes representing different throttle reasons like
442		powercap, overtemp, supply_fault, overcurrent and occ_reset map to
443		the reasons provided by OCC firmware for throttling the frequency.
444
445What:		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats
446		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/turbo_stat
447		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/sub_turbo_stat
448		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/unthrottle
449		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/powercap
450		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overtemp
451		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/supply_fault
452		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overcurrent
453		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/occ_reset
454Date:		March 2016
455Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
456		Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
457Description:	POWERNV CPUFreq driver's frequency throttle stats directory and
458		attributes
459
460		'policyX/throttle_stats' directory and all the attributes are same as
461		the /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats directory and
462		attributes which give the frequency throttle information of the chip.
463
464What:		/sys/devices/system/cpu/cpuX/regs/
465		/sys/devices/system/cpu/cpuX/regs/identification/
466		/sys/devices/system/cpu/cpuX/regs/identification/midr_el1
467		/sys/devices/system/cpu/cpuX/regs/identification/revidr_el1
468Date:		June 2016
469Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
470Description:	AArch64 CPU registers
471		'identification' directory exposes the CPU ID registers for
472		 identifying model and revision of the CPU.
473
474What:		/sys/devices/system/cpu/cpu#/cpu_capacity
475Date:		December 2016
476Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
477Description:	information about CPUs heterogeneity.
478
479		cpu_capacity: capacity of cpu#.
480
481What:		/sys/devices/system/cpu/vulnerabilities
482		/sys/devices/system/cpu/vulnerabilities/meltdown
483		/sys/devices/system/cpu/vulnerabilities/spectre_v1
484		/sys/devices/system/cpu/vulnerabilities/spectre_v2
485		/sys/devices/system/cpu/vulnerabilities/spec_store_bypass
486		/sys/devices/system/cpu/vulnerabilities/l1tf
487		/sys/devices/system/cpu/vulnerabilities/mds
488Date:		January 2018
489Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
490Description:	Information about CPU vulnerabilities
491
492		The files are named after the code names of CPU
493		vulnerabilities. The output of those files reflects the
494		state of the CPUs in the system. Possible output values:
495
496		"Not affected"	  CPU is not affected by the vulnerability
497		"Vulnerable"	  CPU is affected and no mitigation in effect
498		"Mitigation: $M"  CPU is affected and mitigation $M is in effect
499
500		See also: Documentation/admin-guide/hw-vuln/index.rst
501
502What:		/sys/devices/system/cpu/smt
503		/sys/devices/system/cpu/smt/active
504		/sys/devices/system/cpu/smt/control
505Date:		June 2018
506Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
507Description:	Control Symetric Multi Threading (SMT)
508
509		active:  Tells whether SMT is active (enabled and siblings online)
510
511		control: Read/write interface to control SMT. Possible
512			 values:
513
514			 "on"		  SMT is enabled
515			 "off"		  SMT is disabled
516			 "forceoff"	  SMT is force disabled. Cannot be changed.
517			 "notsupported"   SMT is not supported by the CPU
518			 "notimplemented" SMT runtime toggling is not
519					  implemented for the architecture
520
521			 If control status is "forceoff" or "notsupported" writes
522			 are rejected.
523
524What:		/sys/devices/system/cpu/cpu#/power/energy_perf_bias
525Date:		March 2019
526Contact:	linux-pm@vger.kernel.org
527Description:	Intel Energy and Performance Bias Hint (EPB)
528
529		EPB for the given CPU in a sliding scale 0 - 15, where a value
530		of 0 corresponds to a hint preference for highest performance
531		and a value of 15 corresponds to the maximum energy savings.
532
533		In order to change the EPB value for the CPU, write either
534		a number in the 0 - 15 sliding scale above, or one of the
535		strings: "performance", "balance-performance", "normal",
536		"balance-power", "power" (that represent values reflected by
537		their meaning), to this attribute.
538
539		This attribute is present for all online CPUs supporting the
540		Intel EPB feature.
541