Documentation/ABI/testing/sysfs-devices-system-cpu

   1 What:           /sys/devices/system/cpu/
   2 Date:           pre-git history
   3 Contact:        Linux kernel mailing list <[email protected]>
   4 Description:
   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
  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
  17 Date:           December 2008
  18 Contact:        Linux kernel mailing list <[email protected]>
  19 Description:    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
  40 What:           /sys/devices/system/cpu/probe
  41                 /sys/devices/system/cpu/release
  42 Date:           November 2009
  43 Contact:        Linux kernel mailing list <[email protected]>
  44 Description:    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
  56 What:           /sys/devices/system/cpu/cpuX/node
  57 Date:           October 2009
  58 Contact:        Linux memory management mailing list <[email protected]>
  59 Description:    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
  70 What:           /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
  76 Date:           December 2008
  77 Contact:        Linux kernel mailing list <[email protected]>
  78 Description:    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
 110 What:           /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
 114 Date:           September 2007
 115 Contact:        Linux kernel mailing list <[email protected]>
 116 Description:    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
 139 What:           /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
 146 Date:           September 2007
 147 KernelVersion:  v2.6.24
 148 Contact:        Linux power management list <[email protected]>
 149 Description:
 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
 178 What:           /sys/devices/system/cpu/cpuX/cpuidle/state<N>/desc
 179 Date:           February 2008
 180 KernelVersion:  v2.6.25
 181 Contact:        Linux power management list <[email protected]>
 182 Description:
 183                 (RO) A small description about the idle state (string).
 184
 185
 186 What:           /sys/devices/system/cpu/cpuX/cpuidle/state<N>/disable
 187 Date:           March 2012
 188 KernelVersion:  v3.10
 189 Contact:        Linux power management list <[email protected]>
 190 Description:
 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 What:           /sys/devices/system/cpu/cpuX/cpuidle/state<N>/default_status
 200 Date:           December 2019
 201 KernelVersion:  v5.6
 202 Contact:        Linux power management list <[email protected]>
 203 Description:
 204                 (RO) The default status of this state, "enabled" or "disabled".
 205
 206 What:           /sys/devices/system/cpu/cpuX/cpuidle/state<N>/residency
 207 Date:           March 2014
 208 KernelVersion:  v3.15
 209 Contact:        Linux power management list <[email protected]>
 210 Description:
 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
 215 What:           /sys/devices/system/cpu/cpuX/cpuidle/state<N>/s2idle/
 216 Date:           March 2018
 217 KernelVersion:  v4.17
 218 Contact:        Linux power management list <[email protected]>
 219 Description:
 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
 225 What:           /sys/devices/system/cpu/cpuX/cpuidle/state<N>/s2idle/time
 226 Date:           March 2018
 227 KernelVersion:  v4.17
 228 Contact:        Linux power management list <[email protected]>
 229 Description:
 230                 Total time spent by the CPU in suspend-to-idle (with scheduler
 231                 tick suspended) after requesting this state.
 232
 233 What:           /sys/devices/system/cpu/cpuX/cpuidle/state<N>/s2idle/usage
 234 Date:           March 2018
 235 KernelVersion:  v4.17
 236 Contact:        Linux power management list <[email protected]>
 237 Description:
 238                 Total number of times this state has been requested by the CPU
 239                 while entering suspend-to-idle.
 240
 241 What:           /sys/devices/system/cpu/cpuX/cpufreq/*
 242 Date:           pre-git history
 243 Contact:        [email protected]
 244 Description:    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
 256 What:           /sys/devices/system/cpu/cpuX/cpufreq/freqdomain_cpus
 257 Date:           June 2013
 258 Contact:        [email protected]
 259 Description:    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
 272 What:           /sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
 273 Date:           August 2008
 274 KernelVersion:  2.6.27
 275 Contact:        Linux kernel mailing list <[email protected]>
 276 Description:    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
 292 What:           /sys/devices/system/cpu/cpufreq/boost
 293 Date:           August 2012
 294 Contact:        Linux kernel mailing list <[email protected]>
 295 Description:    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
 305 What:           /sys/devices/system/cpu/cpuX/crash_notes
 306                 /sys/devices/system/cpu/cpuX/crash_notes_size
 307 Date:           April 2013
 308 Contact:        [email protected]
 309 Description:    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
 317 What:           /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
 320 Date:           February 2013
 321 Contact:        [email protected]
 322 Description:    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
 341 What:           /sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below>
 342 Date:           July 2014(documented, existed before August 2008)
 343 Contact:        Sudeep Holla <[email protected]>
 344                 Linux kernel mailing list <[email protected]>
 345 Description:    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
 403 What:           /sys/devices/system/cpu/cpu*/cache/index*/id
 404 Date:           September 2016
 405 Contact:        Linux kernel mailing list <[email protected]>
 406 Description:    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
 418 What:           /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
 427 Date:           March 2016
 428 Contact:        Linux kernel mailing list <[email protected]>
 429                 Linux for PowerPC mailing list <[email protected]>
 430 Description:    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
 468 What:           /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
 477 Date:           March 2016
 478 Contact:        Linux kernel mailing list <[email protected]>
 479                 Linux for PowerPC mailing list <[email protected]>
 480 Description:    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
 487 What:           /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
 492 Date:           June 2016
 493 Contact:        Linux ARM Kernel Mailing list <[email protected]>
 494 Description:    AArch64 CPU registers
 495
 496                 'identification' directory exposes the CPU ID registers for
 497                 identifying model and revision of the CPU and SMCU.
 498
 499 What:           /sys/devices/system/cpu/aarch32_el0
 500 Date:           May 2021
 501 Contact:        Linux ARM Kernel Mailing list <[email protected]>
 502 Description:    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
 508 What:           /sys/devices/system/cpu/cpuX/cpu_capacity
 509 Date:           December 2016
 510 Contact:        Linux kernel mailing list <[email protected]>
 511 Description:    information about CPUs heterogeneity.
 512
 513                 cpu_capacity: capacity of cpuX.
 514
 515 What:           /sys/devices/system/cpu/vulnerabilities
 516                 /sys/devices/system/cpu/vulnerabilities/meltdown
 517                 /sys/devices/system/cpu/vulnerabilities/spectre_v1
 518                 /sys/devices/system/cpu/vulnerabilities/spectre_v2
 519                 /sys/devices/system/cpu/vulnerabilities/spec_store_bypass
 520                 /sys/devices/system/cpu/vulnerabilities/l1tf
 521                 /sys/devices/system/cpu/vulnerabilities/mds
 522                 /sys/devices/system/cpu/vulnerabilities/srbds
 523                 /sys/devices/system/cpu/vulnerabilities/tsx_async_abort
 524                 /sys/devices/system/cpu/vulnerabilities/itlb_multihit
 525                 /sys/devices/system/cpu/vulnerabilities/mmio_stale_data
 526                 /sys/devices/system/cpu/vulnerabilities/retbleed
 527 Date:           January 2018
 528 Contact:        Linux kernel mailing list <[email protected]>
 529 Description:    Information about CPU vulnerabilities
 530
 531                 The files are named after the code names of CPU
 532                 vulnerabilities. The output of those files reflects the
 533                 state of the CPUs in the system. Possible output values:
 534
 535                 ================  ==============================================
 536                 "Not affected"    CPU is not affected by the vulnerability
 537                 "Vulnerable"      CPU is affected and no mitigation in effect
 538                 "Mitigation: $M"  CPU is affected and mitigation $M is in effect
 539                 ================  ==============================================
 540
 541                 See also: Documentation/admin-guide/hw-vuln/index.rst
 542
 543 What:           /sys/devices/system/cpu/smt
 544                 /sys/devices/system/cpu/smt/active
 545                 /sys/devices/system/cpu/smt/control
 546 Date:           June 2018
 547 Contact:        Linux kernel mailing list <[email protected]>
 548 Description:    Control Symmetric Multi Threading (SMT)
 549
 550                 active:  Tells whether SMT is active (enabled and siblings online)
 551
 552                 control: Read/write interface to control SMT. Possible
 553                          values:
 554
 555                          ================ =========================================
 556                          "on"             SMT is enabled
 557                          "off"            SMT is disabled
 558                          "forceoff"       SMT is force disabled. Cannot be changed.
 559                          "notsupported"   SMT is not supported by the CPU
 560                          "notimplemented" SMT runtime toggling is not
 561                                           implemented for the architecture
 562                          ================ =========================================
 563
 564                          If control status is "forceoff" or "notsupported" writes
 565                          are rejected.
 566
 567 What:           /sys/devices/system/cpu/cpuX/power/energy_perf_bias
 568 Date:           March 2019
 569 Contact:        [email protected]
 570 Description:    Intel Energy and Performance Bias Hint (EPB)
 571
 572                 EPB for the given CPU in a sliding scale 0 - 15, where a value
 573                 of 0 corresponds to a hint preference for highest performance
 574                 and a value of 15 corresponds to the maximum energy savings.
 575
 576                 In order to change the EPB value for the CPU, write either
 577                 a number in the 0 - 15 sliding scale above, or one of the
 578                 strings: "performance", "balance-performance", "normal",
 579                 "balance-power", "power" (that represent values reflected by
 580                 their meaning), to this attribute.
 581
 582                 This attribute is present for all online CPUs supporting the
 583                 Intel EPB feature.
 584
 585 What:           /sys/devices/system/cpu/umwait_control
 586                 /sys/devices/system/cpu/umwait_control/enable_c02
 587                 /sys/devices/system/cpu/umwait_control/max_time
 588 Date:           May 2019
 589 Contact:        Linux kernel mailing list <[email protected]>
 590 Description:    Umwait control
 591
 592                 enable_c02: Read/write interface to control umwait C0.2 state
 593                         Read returns C0.2 state status:
 594                                 0: C0.2 is disabled
 595                                 1: C0.2 is enabled
 596
 597                         Write 'y' or '1'  or 'on' to enable C0.2 state.
 598                         Write 'n' or '0'  or 'off' to disable C0.2 state.
 599
 600                         The interface is case insensitive.
 601
 602                 max_time: Read/write interface to control umwait maximum time
 603                           in TSC-quanta that the CPU can reside in either C0.1
 604                           or C0.2 state. The time is an unsigned 32-bit number.
 605                           Note that a value of zero means there is no limit.
 606                           Low order two bits must be zero.
 607
 608 What:           /sys/devices/system/cpu/svm
 609 Date:           August 2019
 610 Contact:        Linux kernel mailing list <[email protected]>
 611                 Linux for PowerPC mailing list <[email protected]>
 612 Description:    Secure Virtual Machine
 613
 614                 If 1, it means the system is using the Protected Execution
 615                 Facility in POWER9 and newer processors. i.e., it is a Secure
 616                 Virtual Machine.
 617
 618 What:           /sys/devices/system/cpu/cpuX/purr
 619 Date:           Apr 2005
 620 Contact:        Linux for PowerPC mailing list <[email protected]>
 621 Description:    PURR ticks for this CPU since the system boot.
 622
 623                 The Processor Utilization Resources Register (PURR) is
 624                 a 64-bit counter which provides an estimate of the
 625                 resources used by the CPU thread. The contents of this
 626                 register increases monotonically. This sysfs interface
 627                 exposes the number of PURR ticks for cpuX.
 628
 629 What:           /sys/devices/system/cpu/cpuX/spurr
 630 Date:           Dec 2006
 631 Contact:        Linux for PowerPC mailing list <[email protected]>
 632 Description:    SPURR ticks for this CPU since the system boot.
 633
 634                 The Scaled Processor Utilization Resources Register
 635                 (SPURR) is a 64-bit counter that provides a frequency
 636                 invariant estimate of the resources used by the CPU
 637                 thread. The contents of this register increases
 638                 monotonically. This sysfs interface exposes the number
 639                 of SPURR ticks for cpuX.
 640
 641 What:           /sys/devices/system/cpu/cpuX/idle_purr
 642 Date:           Apr 2020
 643 Contact:        Linux for PowerPC mailing list <[email protected]>
 644 Description:    PURR ticks for cpuX when it was idle.
 645
 646                 This sysfs interface exposes the number of PURR ticks
 647                 for cpuX when it was idle.
 648
 649 What:           /sys/devices/system/cpu/cpuX/idle_spurr
 650 Date:           Apr 2020
 651 Contact:        Linux for PowerPC mailing list <[email protected]>
 652 Description:    SPURR ticks for cpuX when it was idle.
 653
 654                 This sysfs interface exposes the number of SPURR ticks
 655                 for cpuX when it was idle.
 656
 657 What:           /sys/devices/system/cpu/cpuX/mte_tcf_preferred
 658 Date:           July 2021
 659 Contact:        Linux ARM Kernel Mailing list <[email protected]>
 660 Description:    Preferred MTE tag checking mode
 661
 662                 When a user program specifies more than one MTE tag checking
 663                 mode, this sysfs node is used to specify which mode should
 664                 be preferred when scheduling a task on that CPU. Possible
 665                 values:
 666
 667                 ================  ==============================================
 668                 "sync"            Prefer synchronous mode
 669                 "asymm"           Prefer asymmetric mode
 670                 "async"           Prefer asynchronous mode
 671                 ================  ==============================================
 672
 673                 See also: Documentation/arm64/memory-tagging-extension.rst
 674
 675 What:           /sys/devices/system/cpu/nohz_full
 676 Date:           Apr 2015
 677 Contact:        Linux kernel mailing list <[email protected]>
 678 Description:
 679                 (RO) the list of CPUs that are in nohz_full mode.
 680                 These CPUs are set by boot parameter "nohz_full=".
 681
 682 What:           /sys/devices/system/cpu/isolated
 683 Date:           Apr 2015
 684 Contact:        Linux kernel mailing list <[email protected]>
 685 Description:
 686                 (RO) the list of CPUs that are isolated and don't
 687                 participate in load balancing. These CPUs are set by
 688                 boot parameter "isolcpus=".