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/admin-guide/cputopology.rst 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/admin-guide/cputopology.rst 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 Documentation/admin-guide/pm/cpuidle.rst and
141		Documentation/driver-api/pm/cpuidle.rst for more information.
142
143
144What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/name
145		/sys/devices/system/cpu/cpuX/cpuidle/stateN/latency
146		/sys/devices/system/cpu/cpuX/cpuidle/stateN/power
147		/sys/devices/system/cpu/cpuX/cpuidle/stateN/time
148		/sys/devices/system/cpu/cpuX/cpuidle/stateN/usage
149		/sys/devices/system/cpu/cpuX/cpuidle/stateN/above
150		/sys/devices/system/cpu/cpuX/cpuidle/stateN/below
151Date:		September 2007
152KernelVersion:	v2.6.24
153Contact:	Linux power management list <linux-pm@vger.kernel.org>
154Description:
155		The directory /sys/devices/system/cpu/cpuX/cpuidle contains per
156		logical CPU specific cpuidle information for each online cpu X.
157		The processor idle states which are available for use have the
158		following attributes:
159
160		name: (RO) Name of the idle state (string).
161
162		latency: (RO) The latency to exit out of this idle state (in
163		microseconds).
164
165		power: (RO) The power consumed while in this idle state (in
166		milliwatts).
167
168		time: (RO) The total time spent in this idle state (in microseconds).
169
170		usage: (RO) Number of times this state was entered (a count).
171
172		above: (RO) Number of times this state was entered, but the
173		       observed CPU idle duration was too short for it (a count).
174
175		below: (RO) Number of times this state was entered, but the
176		       observed CPU idle duration was too long for it (a count).
177
178What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/desc
179Date:		February 2008
180KernelVersion:	v2.6.25
181Contact:	Linux power management list <linux-pm@vger.kernel.org>
182Description:
183		(RO) A small description about the idle state (string).
184
185
186What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/disable
187Date:		March 2012
188KernelVersion:	v3.10
189Contact:	Linux power management list <linux-pm@vger.kernel.org>
190Description:
191		(RW) Option to disable this idle state (bool). The behavior and
192		the effect of the disable variable depends on the implementation
193		of a particular governor. In the ladder governor, for example,
194		it is not coherent, i.e. if one is disabling a light state, then
195		all deeper states are disabled as well, but the disable variable
196		does not reflect it. Likewise, if one enables a deep state but a
197		lighter state still is disabled, then this has no effect.
198
199
200What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/residency
201Date:		March 2014
202KernelVersion:	v3.15
203Contact:	Linux power management list <linux-pm@vger.kernel.org>
204Description:
205		(RO) Display the target residency i.e. the minimum amount of
206		time (in microseconds) this cpu should spend in this idle state
207		to make the transition worth the effort.
208
209What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/s2idle/
210Date:		March 2018
211KernelVersion:	v4.17
212Contact:	Linux power management list <linux-pm@vger.kernel.org>
213Description:
214		Idle state usage statistics related to suspend-to-idle.
215
216		This attribute group is only present for states that can be
217		used in suspend-to-idle with suspended timekeeping.
218
219What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/s2idle/time
220Date:		March 2018
221KernelVersion:	v4.17
222Contact:	Linux power management list <linux-pm@vger.kernel.org>
223Description:
224		Total time spent by the CPU in suspend-to-idle (with scheduler
225		tick suspended) after requesting this state.
226
227What:		/sys/devices/system/cpu/cpuX/cpuidle/stateN/s2idle/usage
228Date:		March 2018
229KernelVersion:	v4.17
230Contact:	Linux power management list <linux-pm@vger.kernel.org>
231Description:
232		Total number of times this state has been requested by the CPU
233		while entering suspend-to-idle.
234
235What:		/sys/devices/system/cpu/cpu#/cpufreq/*
236Date:		pre-git history
237Contact:	linux-pm@vger.kernel.org
238Description:	Discover and change clock speed of CPUs
239
240		Clock scaling allows you to change the clock speed of the
241		CPUs on the fly. This is a nice method to save battery
242		power, because the lower the clock speed, the less power
243		the CPU consumes.
244
245		There are many knobs to tweak in this directory.
246
247		See files in Documentation/cpu-freq/ for more information.
248
249
250What:		/sys/devices/system/cpu/cpu#/cpufreq/freqdomain_cpus
251Date:		June 2013
252Contact:	linux-pm@vger.kernel.org
253Description:	Discover CPUs in the same CPU frequency coordination domain
254
255		freqdomain_cpus is the list of CPUs (online+offline) that share
256		the same clock/freq domain (possibly at the hardware level).
257		That information may be hidden from the cpufreq core and the
258		value of related_cpus may be different from freqdomain_cpus. This
259		attribute is useful for user space DVFS controllers to get better
260		power/performance results for platforms using acpi-cpufreq.
261
262		This file is only present if the acpi-cpufreq driver is in use.
263
264
265What:		/sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
266Date:		August 2008
267KernelVersion:	2.6.27
268Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
269Description:	Disable L3 cache indices
270
271		These files exist in every CPU's cache/index3 directory. Each
272		cache_disable_{0,1} file corresponds to one disable slot which
273		can be used to disable a cache index. Reading from these files
274		on a processor with this functionality will return the currently
275		disabled index for that node. There is one L3 structure per
276		node, or per internal node on MCM machines. Writing a valid
277		index to one of these files will cause the specificed cache
278		index to be disabled.
279
280		All AMD processors with L3 caches provide this functionality.
281		For details, see BKDGs at
282		http://developer.amd.com/documentation/guides/Pages/default.aspx
283
284
285What:		/sys/devices/system/cpu/cpufreq/boost
286Date:		August 2012
287Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
288Description:	Processor frequency boosting control
289
290		This switch controls the boost setting for the whole system.
291		Boosting allows the CPU and the firmware to run at a frequency
292		beyound it's nominal limit.
293		More details can be found in
294		Documentation/admin-guide/pm/cpufreq.rst
295
296
297What:		/sys/devices/system/cpu/cpu#/crash_notes
298		/sys/devices/system/cpu/cpu#/crash_notes_size
299Date:		April 2013
300Contact:	kexec@lists.infradead.org
301Description:	address and size of the percpu note.
302
303		crash_notes: the physical address of the memory that holds the
304		note of cpu#.
305
306		crash_notes_size: size of the note of cpu#.
307
308
309What:		/sys/devices/system/cpu/intel_pstate/max_perf_pct
310		/sys/devices/system/cpu/intel_pstate/min_perf_pct
311		/sys/devices/system/cpu/intel_pstate/no_turbo
312Date:		February 2013
313Contact:	linux-pm@vger.kernel.org
314Description:	Parameters for the Intel P-state driver
315
316		Logic for selecting the current P-state in Intel
317		Sandybridge+ processors. The three knobs control
318		limits for the P-state that will be requested by the
319		driver.
320
321		max_perf_pct: limits the maximum P state that will be requested by
322		the driver stated as a percentage of the available performance.
323
324		min_perf_pct: limits the minimum P state that will be requested by
325		the driver stated as a percentage of the available performance.
326
327		no_turbo: limits the driver to selecting P states below the turbo
328		frequency range.
329
330		More details can be found in
331		Documentation/admin-guide/pm/intel_pstate.rst
332
333What:		/sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below>
334Date:		July 2014(documented, existed before August 2008)
335Contact:	Sudeep Holla <sudeep.holla@arm.com>
336		Linux kernel mailing list <linux-kernel@vger.kernel.org>
337Description:	Parameters for the CPU cache attributes
338
339		allocation_policy:
340			- WriteAllocate: allocate a memory location to a cache line
341					 on a cache miss because of a write
342			- ReadAllocate: allocate a memory location to a cache line
343					on a cache miss because of a read
344			- ReadWriteAllocate: both writeallocate and readallocate
345
346		attributes: LEGACY used only on IA64 and is same as write_policy
347
348		coherency_line_size: the minimum amount of data in bytes that gets
349				     transferred from memory to cache
350
351		level: the cache hierarchy in the multi-level cache configuration
352
353		number_of_sets: total number of sets in the cache, a set is a
354				collection of cache lines with the same cache index
355
356		physical_line_partition: number of physical cache line per cache tag
357
358		shared_cpu_list: the list of logical cpus sharing the cache
359
360		shared_cpu_map: logical cpu mask containing the list of cpus sharing
361				the cache
362
363		size: the total cache size in kB
364
365		type:
366			- Instruction: cache that only holds instructions
367			- Data: cache that only caches data
368			- Unified: cache that holds both data and instructions
369
370		ways_of_associativity: degree of freedom in placing a particular block
371					of memory in the cache
372
373		write_policy:
374			- WriteThrough: data is written to both the cache line
375					and to the block in the lower-level memory
376			- WriteBack: data is written only to the cache line and
377				     the modified cache line is written to main
378				     memory only when it is replaced
379
380
381What:		/sys/devices/system/cpu/cpu*/cache/index*/id
382Date:		September 2016
383Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
384Description:	Cache id
385
386		The id provides a unique number for a specific instance of
387		a cache of a particular type. E.g. there may be a level
388		3 unified cache on each socket in a server and we may
389		assign them ids 0, 1, 2, ...
390
391		Note that id value can be non-contiguous. E.g. level 1
392		caches typically exist per core, but there may not be a
393		power of two cores on a socket, so these caches may be
394		numbered 0, 1, 2, 3, 4, 5, 8, 9, 10, ...
395
396What:		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats
397		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/turbo_stat
398		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/sub_turbo_stat
399		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/unthrottle
400		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/powercap
401		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overtemp
402		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/supply_fault
403		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overcurrent
404		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/occ_reset
405Date:		March 2016
406Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
407		Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
408Description:	POWERNV CPUFreq driver's frequency throttle stats directory and
409		attributes
410
411		'cpuX/cpufreq/throttle_stats' directory contains the CPU frequency
412		throttle stat attributes for the chip. The throttle stats of a cpu
413		is common across all the cpus belonging to a chip. Below are the
414		throttle attributes exported in the 'throttle_stats' directory:
415
416		- turbo_stat : This file gives the total number of times the max
417		frequency is throttled to lower frequency in turbo (at and above
418		nominal frequency) range of frequencies.
419
420		- sub_turbo_stat : This file gives the total number of times the
421		max frequency is throttled to lower frequency in sub-turbo(below
422		nominal frequency) range of frequencies.
423
424		- unthrottle : This file gives the total number of times the max
425		frequency is unthrottled after being throttled.
426
427		- powercap : This file gives the total number of times the max
428		frequency is throttled due to 'Power Capping'.
429
430		- overtemp : This file gives the total number of times the max
431		frequency is throttled due to 'CPU Over Temperature'.
432
433		- supply_fault : This file gives the total number of times the
434		max frequency is throttled due to 'Power Supply Failure'.
435
436		- overcurrent : This file gives the total number of times the
437		max frequency is throttled due to 'Overcurrent'.
438
439		- occ_reset : This file gives the total number of times the max
440		frequency is throttled due to 'OCC Reset'.
441
442		The sysfs attributes representing different throttle reasons like
443		powercap, overtemp, supply_fault, overcurrent and occ_reset map to
444		the reasons provided by OCC firmware for throttling the frequency.
445
446What:		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats
447		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/turbo_stat
448		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/sub_turbo_stat
449		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/unthrottle
450		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/powercap
451		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overtemp
452		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/supply_fault
453		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overcurrent
454		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/occ_reset
455Date:		March 2016
456Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
457		Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
458Description:	POWERNV CPUFreq driver's frequency throttle stats directory and
459		attributes
460
461		'policyX/throttle_stats' directory and all the attributes are same as
462		the /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats directory and
463		attributes which give the frequency throttle information of the chip.
464
465What:		/sys/devices/system/cpu/cpuX/regs/
466		/sys/devices/system/cpu/cpuX/regs/identification/
467		/sys/devices/system/cpu/cpuX/regs/identification/midr_el1
468		/sys/devices/system/cpu/cpuX/regs/identification/revidr_el1
469Date:		June 2016
470Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
471Description:	AArch64 CPU registers
472		'identification' directory exposes the CPU ID registers for
473		 identifying model and revision of the CPU.
474
475What:		/sys/devices/system/cpu/cpu#/cpu_capacity
476Date:		December 2016
477Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
478Description:	information about CPUs heterogeneity.
479
480		cpu_capacity: capacity of cpu#.
481
482What:		/sys/devices/system/cpu/vulnerabilities
483		/sys/devices/system/cpu/vulnerabilities/meltdown
484		/sys/devices/system/cpu/vulnerabilities/spectre_v1
485		/sys/devices/system/cpu/vulnerabilities/spectre_v2
486		/sys/devices/system/cpu/vulnerabilities/spec_store_bypass
487		/sys/devices/system/cpu/vulnerabilities/l1tf
488		/sys/devices/system/cpu/vulnerabilities/mds
489Date:		January 2018
490Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
491Description:	Information about CPU vulnerabilities
492
493		The files are named after the code names of CPU
494		vulnerabilities. The output of those files reflects the
495		state of the CPUs in the system. Possible output values:
496
497		"Not affected"	  CPU is not affected by the vulnerability
498		"Vulnerable"	  CPU is affected and no mitigation in effect
499		"Mitigation: $M"  CPU is affected and mitigation $M is in effect
500
501		See also: Documentation/admin-guide/hw-vuln/index.rst
502
503What:		/sys/devices/system/cpu/smt
504		/sys/devices/system/cpu/smt/active
505		/sys/devices/system/cpu/smt/control
506Date:		June 2018
507Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
508Description:	Control Symetric Multi Threading (SMT)
509
510		active:  Tells whether SMT is active (enabled and siblings online)
511
512		control: Read/write interface to control SMT. Possible
513			 values:
514
515			 "on"		  SMT is enabled
516			 "off"		  SMT is disabled
517			 "forceoff"	  SMT is force disabled. Cannot be changed.
518			 "notsupported"   SMT is not supported by the CPU
519			 "notimplemented" SMT runtime toggling is not
520					  implemented for the architecture
521
522			 If control status is "forceoff" or "notsupported" writes
523			 are rejected.
524
525What:		/sys/devices/system/cpu/cpu#/power/energy_perf_bias
526Date:		March 2019
527Contact:	linux-pm@vger.kernel.org
528Description:	Intel Energy and Performance Bias Hint (EPB)
529
530		EPB for the given CPU in a sliding scale 0 - 15, where a value
531		of 0 corresponds to a hint preference for highest performance
532		and a value of 15 corresponds to the maximum energy savings.
533
534		In order to change the EPB value for the CPU, write either
535		a number in the 0 - 15 sliding scale above, or one of the
536		strings: "performance", "balance-performance", "normal",
537		"balance-power", "power" (that represent values reflected by
538		their meaning), to this attribute.
539
540		This attribute is present for all online CPUs supporting the
541		Intel EPB feature.
542
543What:		/sys/devices/system/cpu/umwait_control
544		/sys/devices/system/cpu/umwait_control/enable_c02
545		/sys/devices/system/cpu/umwait_control/max_time
546Date:		May 2019
547Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
548Description:	Umwait control
549
550		enable_c02: Read/write interface to control umwait C0.2 state
551			Read returns C0.2 state status:
552				0: C0.2 is disabled
553				1: C0.2 is enabled
554
555			Write 'y' or '1'  or 'on' to enable C0.2 state.
556			Write 'n' or '0'  or 'off' to disable C0.2 state.
557
558			The interface is case insensitive.
559
560		max_time: Read/write interface to control umwait maximum time
561			  in TSC-quanta that the CPU can reside in either C0.1
562			  or C0.2 state. The time is an unsigned 32-bit number.
563			  Note that a value of zero means there is no limit.
564			  Low order two bits must be zero.
565