1 What: /sys/devices/system/cpu/
3 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
5 A collection of both global and individual CPU attributes
7 Individual CPU attributes are contained in subdirectories
8 named by the kernel's logical CPU number, e.g.:
10 /sys/devices/system/cpu/cpu#/
12 What: /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
18 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
19 Description: CPU topology files that describe kernel limits related to
22 kernel_max: the maximum cpu index allowed by the kernel
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).
29 online: cpus that are online and being scheduled.
31 possible: cpus that have been allocated resources and can be
32 brought online if they are present.
34 present: cpus that have been identified as being present in
37 See Documentation/cputopology.txt for more information.
40 What: /sys/devices/system/cpu/probe
41 /sys/devices/system/cpu/release
43 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
44 Description: Dynamic addition and removal of CPU's. This is not hotplug
45 removal, this is meant complete removal/addition of the CPU
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.
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.
56 What: /sys/devices/system/cpu/cpu#/node
58 Contact: Linux memory management mailing list <linux-mm@kvack.org>
59 Description: Discover NUMA node a CPU belongs to
61 When CONFIG_NUMA is enabled, a symbolic link that points
62 to the corresponding NUMA node directory.
64 For example, the following symlink is created for cpu42
67 /sys/devices/system/cpu/cpu42/node2 -> ../../node/node2
70 What: /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
77 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
78 Description: CPU topology files that describe a logical CPU's relationship
79 to other cores and threads in the same physical package.
81 One cpu# directory is created per logical CPU in the system,
82 e.g. /sys/devices/system/cpu/cpu42/.
84 Briefly, the files above are:
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.
90 core_siblings: internal kernel map of cpu#'s hardware threads
91 within the same physical_package_id.
93 core_siblings_list: human-readable list of the logical CPU
94 numbers within the same physical_package_id as cpu#.
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.
100 thread_siblings: internel kernel map of cpu#'s hardware
101 threads within the same core as cpu#
103 thread_siblings_list: human-readable list of cpu#'s hardware
104 threads within the same core as cpu#
106 See Documentation/cputopology.txt for more information.
109 What: /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
114 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
115 Description: Discover cpuidle policy and mechanism
117 Various CPUs today support multiple idle levels that are
118 differentiated by varying exit latencies and power
119 consumption during idle.
121 Idle policy (governor) is differentiated from idle mechanism
124 current_driver: (RO) displays current idle mechanism
126 current_governor_ro: (RO) displays current idle policy
128 With the cpuidle_sysfs_switch boot option enabled (meant for
129 developer testing), the following three attributes are visible
132 current_driver: same as described above
134 available_governors: (RO) displays a space separated list of
137 current_governor: (RW) displays current idle policy. Users can
138 switch the governor at runtime by writing to this file.
140 See Documentation/admin-guide/pm/cpuidle.rst and
141 Documentation/driver-api/pm/cpuidle.rst for more information.
144 What: /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
152 KernelVersion: v2.6.24
153 Contact: Linux power management list <linux-pm@vger.kernel.org>
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:
160 name: (RO) Name of the idle state (string).
162 latency: (RO) The latency to exit out of this idle state (in
165 power: (RO) The power consumed while in this idle state (in
168 time: (RO) The total time spent in this idle state (in microseconds).
170 usage: (RO) Number of times this state was entered (a count).
172 above: (RO) Number of times this state was entered, but the
173 observed CPU idle duration was too short for it (a count).
175 below: (RO) Number of times this state was entered, but the
176 observed CPU idle duration was too long for it (a count).
178 What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/desc
180 KernelVersion: v2.6.25
181 Contact: Linux power management list <linux-pm@vger.kernel.org>
183 (RO) A small description about the idle state (string).
186 What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/disable
189 Contact: Linux power management list <linux-pm@vger.kernel.org>
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.
200 What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/residency
203 Contact: Linux power management list <linux-pm@vger.kernel.org>
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.
209 What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/s2idle/
212 Contact: Linux power management list <linux-pm@vger.kernel.org>
214 Idle state usage statistics related to suspend-to-idle.
216 This attribute group is only present for states that can be
217 used in suspend-to-idle with suspended timekeeping.
219 What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/s2idle/time
222 Contact: Linux power management list <linux-pm@vger.kernel.org>
224 Total time spent by the CPU in suspend-to-idle (with scheduler
225 tick suspended) after requesting this state.
227 What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/s2idle/usage
230 Contact: Linux power management list <linux-pm@vger.kernel.org>
232 Total number of times this state has been requested by the CPU
233 while entering suspend-to-idle.
235 What: /sys/devices/system/cpu/cpu#/cpufreq/*
236 Date: pre-git history
237 Contact: linux-pm@vger.kernel.org
238 Description: Discover and change clock speed of CPUs
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
245 There are many knobs to tweak in this directory.
247 See files in Documentation/cpu-freq/ for more information.
250 What: /sys/devices/system/cpu/cpu#/cpufreq/freqdomain_cpus
252 Contact: linux-pm@vger.kernel.org
253 Description: Discover CPUs in the same CPU frequency coordination domain
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.
262 This file is only present if the acpi-cpufreq driver is in use.
265 What: /sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
267 KernelVersion: 2.6.27
268 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
269 Description: Disable L3 cache indices
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.
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
285 What: /sys/devices/system/cpu/cpufreq/boost
287 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
288 Description: Processor frequency boosting control
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
297 What: /sys/devices/system/cpu/cpu#/crash_notes
298 /sys/devices/system/cpu/cpu#/crash_notes_size
300 Contact: kexec@lists.infradead.org
301 Description: address and size of the percpu note.
303 crash_notes: the physical address of the memory that holds the
306 crash_notes_size: size of the note of cpu#.
309 What: /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
313 Contact: linux-pm@vger.kernel.org
314 Description: Parameters for the Intel P-state driver
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
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.
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.
327 no_turbo: limits the driver to selecting P states below the turbo
330 More details can be found in
331 Documentation/admin-guide/pm/intel_pstate.rst
333 What: /sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below>
334 Date: July 2014(documented, existed before August 2008)
335 Contact: Sudeep Holla <sudeep.holla@arm.com>
336 Linux kernel mailing list <linux-kernel@vger.kernel.org>
337 Description: Parameters for the CPU cache attributes
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
346 attributes: LEGACY used only on IA64 and is same as write_policy
348 coherency_line_size: the minimum amount of data in bytes that gets
349 transferred from memory to cache
351 level: the cache hierarchy in the multi-level cache configuration
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
356 physical_line_partition: number of physical cache line per cache tag
358 shared_cpu_list: the list of logical cpus sharing the cache
360 shared_cpu_map: logical cpu mask containing the list of cpus sharing
363 size: the total cache size in kB
366 - Instruction: cache that only holds instructions
367 - Data: cache that only caches data
368 - Unified: cache that holds both data and instructions
370 ways_of_associativity: degree of freedom in placing a particular block
371 of memory in the cache
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
381 What: /sys/devices/system/cpu/cpu*/cache/index*/id
383 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
384 Description: Cache id
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, ...
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, ...
396 What: /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
406 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
407 Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
408 Description: POWERNV CPUFreq driver's frequency throttle stats directory and
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:
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.
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.
424 - unthrottle : This file gives the total number of times the max
425 frequency is unthrottled after being throttled.
427 - powercap : This file gives the total number of times the max
428 frequency is throttled due to 'Power Capping'.
430 - overtemp : This file gives the total number of times the max
431 frequency is throttled due to 'CPU Over Temperature'.
433 - supply_fault : This file gives the total number of times the
434 max frequency is throttled due to 'Power Supply Failure'.
436 - overcurrent : This file gives the total number of times the
437 max frequency is throttled due to 'Overcurrent'.
439 - occ_reset : This file gives the total number of times the max
440 frequency is throttled due to 'OCC Reset'.
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.
446 What: /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
456 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
457 Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
458 Description: POWERNV CPUFreq driver's frequency throttle stats directory and
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.
465 What: /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
470 Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
471 Description: AArch64 CPU registers
472 'identification' directory exposes the CPU ID registers for
473 identifying model and revision of the CPU.
475 What: /sys/devices/system/cpu/cpu#/cpu_capacity
477 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
478 Description: information about CPUs heterogeneity.
480 cpu_capacity: capacity of cpu#.
482 What: /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
490 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
491 Description: Information about CPU vulnerabilities
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:
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
501 See also: Documentation/admin-guide/hw-vuln/index.rst
503 What: /sys/devices/system/cpu/smt
504 /sys/devices/system/cpu/smt/active
505 /sys/devices/system/cpu/smt/control
507 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
508 Description: Control Symetric Multi Threading (SMT)
510 active: Tells whether SMT is active (enabled and siblings online)
512 control: Read/write interface to control SMT. Possible
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
522 If control status is "forceoff" or "notsupported" writes
525 What: /sys/devices/system/cpu/cpu#/power/energy_perf_bias
527 Contact: linux-pm@vger.kernel.org
528 Description: Intel Energy and Performance Bias Hint (EPB)
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.
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.
540 This attribute is present for all online CPUs supporting the
543 What: /sys/devices/system/cpu/umwait_control
544 /sys/devices/system/cpu/umwait_control/enable_c02
545 /sys/devices/system/cpu/umwait_control/max_time
547 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
548 Description: Umwait control
550 enable_c02: Read/write interface to control umwait C0.2 state
551 Read returns C0.2 state status:
555 Write 'y' or '1' or 'on' to enable C0.2 state.
556 Write 'n' or '0' or 'off' to disable C0.2 state.
558 The interface is case insensitive.
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.