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
111Date:		September 2007
112Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
113Description:	Discover cpuidle policy and mechanism
114
115		Various CPUs today support multiple idle levels that are
116		differentiated by varying exit latencies and power
117		consumption during idle.
118
119		Idle policy (governor) is differentiated from idle mechanism
120		(driver)
121
122		current_driver: displays current idle mechanism
123
124		current_governor_ro: displays current idle policy
125
126		See files in Documentation/cpuidle/ for more information.
127
128
129What:		/sys/devices/system/cpu/cpu#/cpufreq/*
130Date:		pre-git history
131Contact:	linux-pm@vger.kernel.org
132Description:	Discover and change clock speed of CPUs
133
134		Clock scaling allows you to change the clock speed of the
135		CPUs on the fly. This is a nice method to save battery
136		power, because the lower the clock speed, the less power
137		the CPU consumes.
138
139		There are many knobs to tweak in this directory.
140
141		See files in Documentation/cpu-freq/ for more information.
142
143		In particular, read Documentation/cpu-freq/user-guide.txt
144		to learn how to control the knobs.
145
146
147What:		/sys/devices/system/cpu/cpu#/cpufreq/freqdomain_cpus
148Date:		June 2013
149Contact:	linux-pm@vger.kernel.org
150Description:	Discover CPUs in the same CPU frequency coordination domain
151
152		freqdomain_cpus is the list of CPUs (online+offline) that share
153		the same clock/freq domain (possibly at the hardware level).
154		That information may be hidden from the cpufreq core and the
155		value of related_cpus may be different from freqdomain_cpus. This
156		attribute is useful for user space DVFS controllers to get better
157		power/performance results for platforms using acpi-cpufreq.
158
159		This file is only present if the acpi-cpufreq driver is in use.
160
161
162What:		/sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
163Date:		August 2008
164KernelVersion:	2.6.27
165Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
166Description:	Disable L3 cache indices
167
168		These files exist in every CPU's cache/index3 directory. Each
169		cache_disable_{0,1} file corresponds to one disable slot which
170		can be used to disable a cache index. Reading from these files
171		on a processor with this functionality will return the currently
172		disabled index for that node. There is one L3 structure per
173		node, or per internal node on MCM machines. Writing a valid
174		index to one of these files will cause the specificed cache
175		index to be disabled.
176
177		All AMD processors with L3 caches provide this functionality.
178		For details, see BKDGs at
179		http://developer.amd.com/documentation/guides/Pages/default.aspx
180
181
182What:		/sys/devices/system/cpu/cpufreq/boost
183Date:		August 2012
184Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
185Description:	Processor frequency boosting control
186
187		This switch controls the boost setting for the whole system.
188		Boosting allows the CPU and the firmware to run at a frequency
189		beyound it's nominal limit.
190		More details can be found in
191		Documentation/admin-guide/pm/cpufreq.rst
192
193
194What:		/sys/devices/system/cpu/cpu#/crash_notes
195		/sys/devices/system/cpu/cpu#/crash_notes_size
196Date:		April 2013
197Contact:	kexec@lists.infradead.org
198Description:	address and size of the percpu note.
199
200		crash_notes: the physical address of the memory that holds the
201		note of cpu#.
202
203		crash_notes_size: size of the note of cpu#.
204
205
206What:		/sys/devices/system/cpu/intel_pstate/max_perf_pct
207		/sys/devices/system/cpu/intel_pstate/min_perf_pct
208		/sys/devices/system/cpu/intel_pstate/no_turbo
209Date:		February 2013
210Contact:	linux-pm@vger.kernel.org
211Description:	Parameters for the Intel P-state driver
212
213		Logic for selecting the current P-state in Intel
214		Sandybridge+ processors. The three knobs control
215		limits for the P-state that will be requested by the
216		driver.
217
218		max_perf_pct: limits the maximum P state that will be requested by
219		the driver stated as a percentage of the available performance.
220
221		min_perf_pct: limits the minimum P state that will be requested by
222		the driver stated as a percentage of the available performance.
223
224		no_turbo: limits the driver to selecting P states below the turbo
225		frequency range.
226
227		More details can be found in
228		Documentation/admin-guide/pm/intel_pstate.rst
229
230What:		/sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below>
231Date:		July 2014(documented, existed before August 2008)
232Contact:	Sudeep Holla <sudeep.holla@arm.com>
233		Linux kernel mailing list <linux-kernel@vger.kernel.org>
234Description:	Parameters for the CPU cache attributes
235
236		allocation_policy:
237			- WriteAllocate: allocate a memory location to a cache line
238					 on a cache miss because of a write
239			- ReadAllocate: allocate a memory location to a cache line
240					on a cache miss because of a read
241			- ReadWriteAllocate: both writeallocate and readallocate
242
243		attributes: LEGACY used only on IA64 and is same as write_policy
244
245		coherency_line_size: the minimum amount of data in bytes that gets
246				     transferred from memory to cache
247
248		level: the cache hierarchy in the multi-level cache configuration
249
250		number_of_sets: total number of sets in the cache, a set is a
251				collection of cache lines with the same cache index
252
253		physical_line_partition: number of physical cache line per cache tag
254
255		shared_cpu_list: the list of logical cpus sharing the cache
256
257		shared_cpu_map: logical cpu mask containing the list of cpus sharing
258				the cache
259
260		size: the total cache size in kB
261
262		type:
263			- Instruction: cache that only holds instructions
264			- Data: cache that only caches data
265			- Unified: cache that holds both data and instructions
266
267		ways_of_associativity: degree of freedom in placing a particular block
268					of memory in the cache
269
270		write_policy:
271			- WriteThrough: data is written to both the cache line
272					and to the block in the lower-level memory
273			- WriteBack: data is written only to the cache line and
274				     the modified cache line is written to main
275				     memory only when it is replaced
276
277
278What:		/sys/devices/system/cpu/cpu*/cache/index*/id
279Date:		September 2016
280Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
281Description:	Cache id
282
283		The id provides a unique number for a specific instance of
284		a cache of a particular type. E.g. there may be a level
285		3 unified cache on each socket in a server and we may
286		assign them ids 0, 1, 2, ...
287
288		Note that id value can be non-contiguous. E.g. level 1
289		caches typically exist per core, but there may not be a
290		power of two cores on a socket, so these caches may be
291		numbered 0, 1, 2, 3, 4, 5, 8, 9, 10, ...
292
293What:		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats
294		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/turbo_stat
295		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/sub_turbo_stat
296		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/unthrottle
297		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/powercap
298		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overtemp
299		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/supply_fault
300		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overcurrent
301		/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/occ_reset
302Date:		March 2016
303Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
304		Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
305Description:	POWERNV CPUFreq driver's frequency throttle stats directory and
306		attributes
307
308		'cpuX/cpufreq/throttle_stats' directory contains the CPU frequency
309		throttle stat attributes for the chip. The throttle stats of a cpu
310		is common across all the cpus belonging to a chip. Below are the
311		throttle attributes exported in the 'throttle_stats' directory:
312
313		- turbo_stat : This file gives the total number of times the max
314		frequency is throttled to lower frequency in turbo (at and above
315		nominal frequency) range of frequencies.
316
317		- sub_turbo_stat : This file gives the total number of times the
318		max frequency is throttled to lower frequency in sub-turbo(below
319		nominal frequency) range of frequencies.
320
321		- unthrottle : This file gives the total number of times the max
322		frequency is unthrottled after being throttled.
323
324		- powercap : This file gives the total number of times the max
325		frequency is throttled due to 'Power Capping'.
326
327		- overtemp : This file gives the total number of times the max
328		frequency is throttled due to 'CPU Over Temperature'.
329
330		- supply_fault : This file gives the total number of times the
331		max frequency is throttled due to 'Power Supply Failure'.
332
333		- overcurrent : This file gives the total number of times the
334		max frequency is throttled due to 'Overcurrent'.
335
336		- occ_reset : This file gives the total number of times the max
337		frequency is throttled due to 'OCC Reset'.
338
339		The sysfs attributes representing different throttle reasons like
340		powercap, overtemp, supply_fault, overcurrent and occ_reset map to
341		the reasons provided by OCC firmware for throttling the frequency.
342
343What:		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats
344		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/turbo_stat
345		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/sub_turbo_stat
346		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/unthrottle
347		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/powercap
348		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overtemp
349		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/supply_fault
350		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overcurrent
351		/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/occ_reset
352Date:		March 2016
353Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
354		Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
355Description:	POWERNV CPUFreq driver's frequency throttle stats directory and
356		attributes
357
358		'policyX/throttle_stats' directory and all the attributes are same as
359		the /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats directory and
360		attributes which give the frequency throttle information of the chip.
361
362What:		/sys/devices/system/cpu/cpuX/regs/
363		/sys/devices/system/cpu/cpuX/regs/identification/
364		/sys/devices/system/cpu/cpuX/regs/identification/midr_el1
365		/sys/devices/system/cpu/cpuX/regs/identification/revidr_el1
366Date:		June 2016
367Contact:	Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
368Description:	AArch64 CPU registers
369		'identification' directory exposes the CPU ID registers for
370		 identifying model and revision of the CPU.
371
372What:		/sys/devices/system/cpu/cpu#/cpu_capacity
373Date:		December 2016
374Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
375Description:	information about CPUs heterogeneity.
376
377		cpu_capacity: capacity of cpu#.
378