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/cpuX/
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 written to the file to remove CPU's
54		is architecture specific.
55
56What:		/sys/devices/system/cpu/cpuX/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/cpuX/topology/core_siblings
71		/sys/devices/system/cpu/cpuX/topology/core_siblings_list
72		/sys/devices/system/cpu/cpuX/topology/physical_package_id
73		/sys/devices/system/cpu/cpuX/topology/thread_siblings
74		/sys/devices/system/cpu/cpuX/topology/thread_siblings_list
75		/sys/devices/system/cpu/cpuX/topology/ppin
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 cpuX 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_siblings: internal kernel map of cpuX's hardware threads
87		within the same physical_package_id.
88
89		core_siblings_list: human-readable list of the logical CPU
90		numbers within the same physical_package_id as cpuX.
91
92		physical_package_id: physical package id of cpuX. Typically
93		corresponds to a physical socket number, but the actual value
94		is architecture and platform dependent.
95
96		thread_siblings: internal kernel map of cpuX's hardware
97		threads within the same core as cpuX
98
99		thread_siblings_list: human-readable list of cpuX's hardware
100		threads within the same core as cpuX
101
102		ppin: human-readable Protected Processor Identification
103		Number of the socket the cpu# belongs to. There should be
104		one per physical_package_id. File is readable only to
105		admin.
106
107		See Documentation/admin-guide/cputopology.rst for more information.
108
109
110What:		/sys/devices/system/cpu/cpuidle/available_governors
111		/sys/devices/system/cpu/cpuidle/current_driver
112		/sys/devices/system/cpu/cpuidle/current_governor
113		/sys/devices/system/cpu/cpuidle/current_governer_ro
114Date:		September 2007
115Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
116Description:	Discover cpuidle policy and mechanism
117
118		Various CPUs today support multiple idle levels that are
119		differentiated by varying exit latencies and power
120		consumption during idle.
121
122		Idle policy (governor) is differentiated from idle mechanism
123		(driver).
124
125		available_governors: (RO) displays a space separated list of
126		available governors.
127
128		current_driver: (RO) displays current idle mechanism.
129
130		current_governor: (RW) displays current idle policy. Users can
131		switch the governor at runtime by writing to this file.
132
133		current_governor_ro: (RO) displays current idle policy.
134
135		See Documentation/admin-guide/pm/cpuidle.rst and
136		Documentation/driver-api/pm/cpuidle.rst for more information.
137
138
139What:		/sys/devices/system/cpu/cpuX/cpuidle/state<N>/name
140		/sys/devices/system/cpu/cpuX/cpuidle/stateN/latency
141		/sys/devices/system/cpu/cpuX/cpuidle/stateN/power
142		/sys/devices/system/cpu/cpuX/cpuidle/stateN/time
143		/sys/devices/system/cpu/cpuX/cpuidle/stateN/usage
144		/sys/devices/system/cpu/cpuX/cpuidle/stateN/above
145		/sys/devices/system/cpu/cpuX/cpuidle/stateN/below
146Date:		September 2007
147KernelVersion:	v2.6.24
148Contact:	Linux power management list <linux-pm@vger.kernel.org>
149Description:
150		The directory /sys/devices/system/cpu/cpuX/cpuidle contains per
151		logical CPU specific cpuidle information for each online cpu X.
152		The processor idle states which are available for use have the
153		following attributes:
154
155		======== ==== =================================================
156		name:	 (RO) Name of the idle state (string).
157
158		latency: (RO) The latency to exit out of this idle state (in
159			      microseconds).
160
161		power:   (RO) The power consumed while in this idle state (in
162			      milliwatts).
163
164		time:    (RO) The total time spent in this idle state
165			      (in microseconds).
166
167		usage:	 (RO) Number of times this state was entered (a count).
168
169		above:	 (RO) Number of times this state was entered, but the
170			      observed CPU idle duration was too short for it
171			      (a count).
172
173		below:	 (RO) Number of times this state was entered, but the
174			      observed CPU idle duration was too long for it
175			      (a count).
176		======== ==== =================================================
177
178What:		/sys/devices/system/cpu/cpuX/cpuidle/state<N>/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/state<N>/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
199What:		/sys/devices/system/cpu/cpuX/cpuidle/state<N>/default_status
200Date:		December 2019
201KernelVersion:	v5.6
202Contact:	Linux power management list <linux-pm@vger.kernel.org>
203Description:
204		(RO) The default status of this state, "enabled" or "disabled".
205
206What:		/sys/devices/system/cpu/cpuX/cpuidle/state<N>/residency
207Date:		March 2014
208KernelVersion:	v3.15
209Contact:	Linux power management list <linux-pm@vger.kernel.org>
210Description:
211		(RO) Display the target residency i.e. the minimum amount of
212		time (in microseconds) this cpu should spend in this idle state
213		to make the transition worth the effort.
214
215What:		/sys/devices/system/cpu/cpuX/cpuidle/state<N>/s2idle/
216Date:		March 2018
217KernelVersion:	v4.17
218Contact:	Linux power management list <linux-pm@vger.kernel.org>
219Description:
220		Idle state usage statistics related to suspend-to-idle.
221
222		This attribute group is only present for states that can be
223		used in suspend-to-idle with suspended timekeeping.
224
225What:		/sys/devices/system/cpu/cpuX/cpuidle/state<N>/s2idle/time
226Date:		March 2018
227KernelVersion:	v4.17
228Contact:	Linux power management list <linux-pm@vger.kernel.org>
229Description:
230		Total time spent by the CPU in suspend-to-idle (with scheduler
231		tick suspended) after requesting this state.
232
233What:		/sys/devices/system/cpu/cpuX/cpuidle/state<N>/s2idle/usage
234Date:		March 2018
235KernelVersion:	v4.17
236Contact:	Linux power management list <linux-pm@vger.kernel.org>
237Description:
238		Total number of times this state has been requested by the CPU
239		while entering suspend-to-idle.
240
241What:		/sys/devices/system/cpu/cpuX/cpufreq/*
242Date:		pre-git history
243Contact:	linux-pm@vger.kernel.org
244Description:	Discover and change clock speed of CPUs
245
246		Clock scaling allows you to change the clock speed of the
247		CPUs on the fly. This is a nice method to save battery
248		power, because the lower the clock speed, the less power
249		the CPU consumes.
250
251		There are many knobs to tweak in this directory.
252
253		See files in Documentation/cpu-freq/ for more information.
254
255
256What:		/sys/devices/system/cpu/cpuX/cpufreq/freqdomain_cpus
257Date:		June 2013
258Contact:	linux-pm@vger.kernel.org
259Description:	Discover CPUs in the same CPU frequency coordination domain
260
261		freqdomain_cpus is the list of CPUs (online+offline) that share
262		the same clock/freq domain (possibly at the hardware level).
263		That information may be hidden from the cpufreq core and the
264		value of related_cpus may be different from freqdomain_cpus. This
265		attribute is useful for user space DVFS controllers to get better
266		power/performance results for platforms using acpi-cpufreq.
267
268		This file is only present if the acpi-cpufreq or the cppc-cpufreq
269		drivers are in use.
270
271
272What:		/sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
273Date:		August 2008
274KernelVersion:	2.6.27
275Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
276Description:	Disable L3 cache indices
277
278		These files exist in every CPU's cache/index3 directory. Each
279		cache_disable_{0,1} file corresponds to one disable slot which
280		can be used to disable a cache index. Reading from these files
281		on a processor with this functionality will return the currently
282		disabled index for that node. There is one L3 structure per
283		node, or per internal node on MCM machines. Writing a valid
284		index to one of these files will cause the specified cache
285		index to be disabled.
286
287		All AMD processors with L3 caches provide this functionality.
288		For details, see BKDGs at
289                https://www.amd.com/en/support/tech-docs?keyword=bios+kernel
290
291
292What:		/sys/devices/system/cpu/cpufreq/boost
293Date:		August 2012
294Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
295Description:	Processor frequency boosting control
296
297		This switch controls the boost setting for the whole system.
298		Boosting allows the CPU and the firmware to run at a frequency
299		beyond its nominal limit.
300
301		More details can be found in
302		Documentation/admin-guide/pm/cpufreq.rst
303
304
305What:		/sys/devices/system/cpu/cpuX/crash_notes
306		/sys/devices/system/cpu/cpuX/crash_notes_size
307Date:		April 2013
308Contact:	kexec@lists.infradead.org
309Description:	address and size of the percpu note.
310
311		crash_notes: the physical address of the memory that holds the
312		note of cpuX.
313
314		crash_notes_size: size of the note of cpuX.
315
316
317What:		/sys/devices/system/cpu/intel_pstate/max_perf_pct
318		/sys/devices/system/cpu/intel_pstate/min_perf_pct
319		/sys/devices/system/cpu/intel_pstate/no_turbo
320Date:		February 2013
321Contact:	linux-pm@vger.kernel.org
322Description:	Parameters for the Intel P-state driver
323
324		Logic for selecting the current P-state in Intel
325		Sandybridge+ processors. The three knobs control
326		limits for the P-state that will be requested by the
327		driver.
328
329		max_perf_pct: limits the maximum P state that will be requested by
330		the driver stated as a percentage of the available performance.
331
332		min_perf_pct: limits the minimum P state that will be requested by
333		the driver stated as a percentage of the available performance.
334
335		no_turbo: limits the driver to selecting P states below the turbo
336		frequency range.
337
338		More details can be found in
339		Documentation/admin-guide/pm/intel_pstate.rst
340
341What:		/sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below>
342Date:		July 2014(documented, existed before August 2008)
343Contact:	Sudeep Holla <sudeep.holla@arm.com>
344		Linux kernel mailing list <linux-kernel@vger.kernel.org>
345Description:	Parameters for the CPU cache attributes
346
347		allocation_policy:
348			- WriteAllocate:
349					allocate a memory location to a cache line
350					on a cache miss because of a write
351			- ReadAllocate:
352					allocate a memory location to a cache line
353					on a cache miss because of a read
354			- ReadWriteAllocate:
355					both writeallocate and readallocate
356
357		attributes:
358			    LEGACY used only on IA64 and is same as write_policy
359
360		coherency_line_size:
361				     the minimum amount of data in bytes that gets
362				     transferred from memory to cache
363
364		level:
365			the cache hierarchy in the multi-level cache configuration
366
367		number_of_sets:
368				total number of sets in the cache, a set is a
369				collection of cache lines with the same cache index
370
371		physical_line_partition:
372				number of physical cache line per cache tag
373
374		shared_cpu_list:
375				the list of logical cpus sharing the cache
376
377		shared_cpu_map:
378				logical cpu mask containing the list of cpus sharing
379				the cache
380
381		size:
382			the total cache size in kB
383
384		type:
385			- Instruction: cache that only holds instructions
386			- Data: cache that only caches data
387			- Unified: cache that holds both data and instructions
388
389		ways_of_associativity:
390			degree of freedom in placing a particular block
391			of memory in the cache
392
393		write_policy:
394			- WriteThrough:
395					data is written to both the cache line
396					and to the block in the lower-level memory
397			- WriteBack:
398				     data is written only to the cache line and
399				     the modified cache line is written to main
400				     memory only when it is replaced
401
402
403What:		/sys/devices/system/cpu/cpu*/cache/index*/id
404Date:		September 2016
405Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
406Description:	Cache id
407
408		The id provides a unique number for a specific instance of
409		a cache of a particular type. E.g. there may be a level
410		3 unified cache on each socket in a server and we may
411		assign them ids 0, 1, 2, ...
412
413		Note that id value can be non-contiguous. E.g. level 1
414		caches typically exist per core, but there may not be a
415		power of two cores on a socket, so these caches may be
416		numbered 0, 1, 2, 3, 4, 5, 8, 9, 10, ...
417
418What:		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats
419		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/turbo_stat
420		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/sub_turbo_stat
421		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/unthrottle
422		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/powercap
423		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overtemp
424		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/supply_fault
425		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overcurrent
426		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/occ_reset
427Date:		March 2016
428Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
429		Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
430Description:	POWERNV CPUFreq driver's frequency throttle stats directory and
431		attributes
432
433		'cpuX/cpufreq/throttle_stats' directory contains the CPU frequency
434		throttle stat attributes for the chip. The throttle stats of a cpu
435		is common across all the cpus belonging to a chip. Below are the
436		throttle attributes exported in the 'throttle_stats' directory:
437
438		- turbo_stat : This file gives the total number of times the max
439		  frequency is throttled to lower frequency in turbo (at and above
440		  nominal frequency) range of frequencies.
441
442		- sub_turbo_stat : This file gives the total number of times the
443		  max frequency is throttled to lower frequency in sub-turbo(below
444		  nominal frequency) range of frequencies.
445
446		- unthrottle : This file gives the total number of times the max
447		  frequency is unthrottled after being throttled.
448
449		- powercap : This file gives the total number of times the max
450		  frequency is throttled due to 'Power Capping'.
451
452		- overtemp : This file gives the total number of times the max
453		  frequency is throttled due to 'CPU Over Temperature'.
454
455		- supply_fault : This file gives the total number of times the
456		  max frequency is throttled due to 'Power Supply Failure'.
457
458		- overcurrent : This file gives the total number of times the
459		  max frequency is throttled due to 'Overcurrent'.
460
461		- occ_reset : This file gives the total number of times the max
462		  frequency is throttled due to 'OCC Reset'.
463
464		The sysfs attributes representing different throttle reasons like
465		powercap, overtemp, supply_fault, overcurrent and occ_reset map to
466		the reasons provided by OCC firmware for throttling the frequency.
467
468What:		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats
469		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/turbo_stat
470		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/sub_turbo_stat
471		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/unthrottle
472		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/powercap
473		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overtemp
474		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/supply_fault
475		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overcurrent
476		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/occ_reset
477Date:		March 2016
478Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
479		Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
480Description:	POWERNV CPUFreq driver's frequency throttle stats directory and
481		attributes
482
483		'policyX/throttle_stats' directory and all the attributes are same as
484		the /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats directory and
485		attributes which give the frequency throttle information of the chip.
486
487What:		/sys/devices/system/cpu/cpuX/regs/
488		/sys/devices/system/cpu/cpuX/regs/identification/
489		/sys/devices/system/cpu/cpuX/regs/identification/midr_el1
490		/sys/devices/system/cpu/cpuX/regs/identification/revidr_el1
491		/sys/devices/system/cpu/cpuX/regs/identification/smidr_el1
492Date:		June 2016
493Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
494Description:	AArch64 CPU registers
495
496		'identification' directory exposes the CPU ID registers for
497		identifying model and revision of the CPU and SMCU.
498
499What:		/sys/devices/system/cpu/aarch32_el0
500Date:		May 2021
501Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
502Description:	Identifies the subset of CPUs in the system that can execute
503		AArch32 (32-bit ARM) applications. If present, the same format as
504		/sys/devices/system/cpu/{offline,online,possible,present} is used.
505		If absent, then all or none of the CPUs can execute AArch32
506		applications and execve() will behave accordingly.
507
508What:		/sys/devices/system/cpu/cpuX/cpu_capacity
509Date:		December 2016
510Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
511Description:	information about CPUs heterogeneity.
512
513		cpu_capacity: capacity of cpuX.
514
515What:		/sys/devices/system/cpu/vulnerabilities
516		/sys/devices/system/cpu/vulnerabilities/gather_data_sampling
517		/sys/devices/system/cpu/vulnerabilities/itlb_multihit
518		/sys/devices/system/cpu/vulnerabilities/l1tf
519		/sys/devices/system/cpu/vulnerabilities/mds
520		/sys/devices/system/cpu/vulnerabilities/meltdown
521		/sys/devices/system/cpu/vulnerabilities/mmio_stale_data
522		/sys/devices/system/cpu/vulnerabilities/reg_file_data_sampling
523		/sys/devices/system/cpu/vulnerabilities/retbleed
524		/sys/devices/system/cpu/vulnerabilities/spec_store_bypass
525		/sys/devices/system/cpu/vulnerabilities/spectre_v1
526		/sys/devices/system/cpu/vulnerabilities/spectre_v2
527		/sys/devices/system/cpu/vulnerabilities/srbds
528		/sys/devices/system/cpu/vulnerabilities/tsx_async_abort
529Date:		January 2018
530Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
531Description:	Information about CPU vulnerabilities
532
533		The files are named after the code names of CPU
534		vulnerabilities. The output of those files reflects the
535		state of the CPUs in the system. Possible output values:
536
537		================  ==============================================
538		"Not affected"	  CPU is not affected by the vulnerability
539		"Vulnerable"	  CPU is affected and no mitigation in effect
540		"Mitigation: $M"  CPU is affected and mitigation $M is in effect
541		================  ==============================================
542
543		See also: Documentation/admin-guide/hw-vuln/index.rst
544
545What:		/sys/devices/system/cpu/smt
546		/sys/devices/system/cpu/smt/active
547		/sys/devices/system/cpu/smt/control
548Date:		June 2018
549Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
550Description:	Control Symmetric Multi Threading (SMT)
551
552		active:  Tells whether SMT is active (enabled and siblings online)
553
554		control: Read/write interface to control SMT. Possible
555			 values:
556
557			 ================ =========================================
558			 "on"		  SMT is enabled
559			 "off"		  SMT is disabled
560			 "<N>"		  SMT is enabled with N threads per core.
561			 "forceoff"	  SMT is force disabled. Cannot be changed.
562			 "notsupported"   SMT is not supported by the CPU
563			 "notimplemented" SMT runtime toggling is not
564					  implemented for the architecture
565			 ================ =========================================
566
567			 If control status is "forceoff" or "notsupported" writes
568			 are rejected. Note that enabling SMT on PowerPC skips
569			 offline cores.
570
571What:		/sys/devices/system/cpu/cpuX/power/energy_perf_bias
572Date:		March 2019
573Contact:	linux-pm@vger.kernel.org
574Description:	Intel Energy and Performance Bias Hint (EPB)
575
576		EPB for the given CPU in a sliding scale 0 - 15, where a value
577		of 0 corresponds to a hint preference for highest performance
578		and a value of 15 corresponds to the maximum energy savings.
579
580		In order to change the EPB value for the CPU, write either
581		a number in the 0 - 15 sliding scale above, or one of the
582		strings: "performance", "balance-performance", "normal",
583		"balance-power", "power" (that represent values reflected by
584		their meaning), to this attribute.
585
586		This attribute is present for all online CPUs supporting the
587		Intel EPB feature.
588
589What:		/sys/devices/system/cpu/umwait_control
590		/sys/devices/system/cpu/umwait_control/enable_c02
591		/sys/devices/system/cpu/umwait_control/max_time
592Date:		May 2019
593Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
594Description:	Umwait control
595
596		enable_c02: Read/write interface to control umwait C0.2 state
597			Read returns C0.2 state status:
598				0: C0.2 is disabled
599				1: C0.2 is enabled
600
601			Write 'y' or '1'  or 'on' to enable C0.2 state.
602			Write 'n' or '0'  or 'off' to disable C0.2 state.
603
604			The interface is case insensitive.
605
606		max_time: Read/write interface to control umwait maximum time
607			  in TSC-quanta that the CPU can reside in either C0.1
608			  or C0.2 state. The time is an unsigned 32-bit number.
609			  Note that a value of zero means there is no limit.
610			  Low order two bits must be zero.
611
612What:		/sys/devices/system/cpu/svm
613Date:		August 2019
614Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
615		Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
616Description:	Secure Virtual Machine
617
618		If 1, it means the system is using the Protected Execution
619		Facility in POWER9 and newer processors. i.e., it is a Secure
620		Virtual Machine.
621
622What:		/sys/devices/system/cpu/cpuX/purr
623Date:		Apr 2005
624Contact:	Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
625Description:	PURR ticks for this CPU since the system boot.
626
627		The Processor Utilization Resources Register (PURR) is
628		a 64-bit counter which provides an estimate of the
629		resources used by the CPU thread. The contents of this
630		register increases monotonically. This sysfs interface
631		exposes the number of PURR ticks for cpuX.
632
633What: 		/sys/devices/system/cpu/cpuX/spurr
634Date:		Dec 2006
635Contact:	Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
636Description:	SPURR ticks for this CPU since the system boot.
637
638		The Scaled Processor Utilization Resources Register
639		(SPURR) is a 64-bit counter that provides a frequency
640		invariant estimate of the resources used by the CPU
641		thread. The contents of this register increases
642		monotonically. This sysfs interface exposes the number
643		of SPURR ticks for cpuX.
644
645What: 		/sys/devices/system/cpu/cpuX/idle_purr
646Date:		Apr 2020
647Contact:	Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
648Description:	PURR ticks for cpuX when it was idle.
649
650		This sysfs interface exposes the number of PURR ticks
651		for cpuX when it was idle.
652
653What: 		/sys/devices/system/cpu/cpuX/idle_spurr
654Date:		Apr 2020
655Contact:	Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
656Description:	SPURR ticks for cpuX when it was idle.
657
658		This sysfs interface exposes the number of SPURR ticks
659		for cpuX when it was idle.
660
661What: 		/sys/devices/system/cpu/cpuX/mte_tcf_preferred
662Date:		July 2021
663Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
664Description:	Preferred MTE tag checking mode
665
666		When a user program specifies more than one MTE tag checking
667		mode, this sysfs node is used to specify which mode should
668		be preferred when scheduling a task on that CPU. Possible
669		values:
670
671		================  ==============================================
672		"sync"	  	  Prefer synchronous mode
673		"asymm"	  	  Prefer asymmetric mode
674		"async"	  	  Prefer asynchronous mode
675		================  ==============================================
676
677		See also: Documentation/arch/arm64/memory-tagging-extension.rst
678
679What:		/sys/devices/system/cpu/nohz_full
680Date:		Apr 2015
681Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
682Description:
683		(RO) the list of CPUs that are in nohz_full mode.
684		These CPUs are set by boot parameter "nohz_full=".
685
686What:		/sys/devices/system/cpu/isolated
687Date:		Apr 2015
688Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
689Description:
690		(RO) the list of CPUs that are isolated and don't
691		participate in load balancing. These CPUs are set by
692		boot parameter "isolcpus=".
693
694What:		/sys/devices/system/cpu/crash_hotplug
695Date:		Aug 2023
696Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
697Description:
698		(RO) indicates whether or not the kernel directly supports
699		modifying the crash elfcorehdr for CPU hot un/plug and/or
700		on/offline changes.
701