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

   1 What:           /sys/devices/system/cpu/
   2 Date:           pre-git history
   3 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
   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/cpu#/
  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 <linux-kernel@vger.kernel.org>
  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 <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
  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
  56 What:           /sys/devices/system/cpu/cpu#/node
  57 Date:           October 2009
  58 Contact:        Linux memory management mailing list <linux-mm@kvack.org>
  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/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
  76 Date:           December 2008
  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.
  80
  81                 One cpu# directory is created per logical CPU in the system,
  82                 e.g. /sys/devices/system/cpu/cpu42/.
  83
  84                 Briefly, the files above are:
  85
  86                 core_id: the CPU core ID of cpu#. Typically it is the
  87                 hardware platform's identifier (rather than the kernel's).
  88                 The actual value is architecture and platform dependent.
  89
  90                 core_siblings: internal kernel map of cpu#'s hardware threads
  91                 within the same physical_package_id.
  92
  93                 core_siblings_list: human-readable list of the logical CPU
  94                 numbers within the same physical_package_id as cpu#.
  95
  96                 physical_package_id: physical package id of cpu#. Typically
  97                 corresponds to a physical socket number, but the actual value
  98                 is architecture and platform dependent.
  99
 100                 thread_siblings: internel kernel map of cpu#'s hardware
 101                 threads within the same core as cpu#
 102
 103                 thread_siblings_list: human-readable list of cpu#'s hardware
 104                 threads within the same core as cpu#
 105
 106                 See Documentation/admin-guide/cputopology.rst for more information.
 107
 108
 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
 113 Date:           September 2007
 114 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 115 Description:    Discover cpuidle policy and mechanism
 116
 117                 Various CPUs today support multiple idle levels that are
 118                 differentiated by varying exit latencies and power
 119                 consumption during idle.
 120
 121                 Idle policy (governor) is differentiated from idle mechanism
 122                 (driver)
 123
 124                 current_driver: (RO) displays current idle mechanism
 125
 126                 current_governor_ro: (RO) displays current idle policy
 127
 128                 With the cpuidle_sysfs_switch boot option enabled (meant for
 129                 developer testing), the following three attributes are visible
 130                 instead:
 131
 132                 current_driver: same as described above
 133
 134                 available_governors: (RO) displays a space separated list of
 135                 available governors
 136
 137                 current_governor: (RW) displays current idle policy. Users can
 138                 switch the governor at runtime by writing to this file.
 139
 140                 See Documentation/admin-guide/pm/cpuidle.rst and
 141                 Documentation/driver-api/pm/cpuidle.rst for more information.
 142
 143
 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
 151 Date:           September 2007
 152 KernelVersion:  v2.6.24
 153 Contact:        Linux power management list <linux-pm@vger.kernel.org>
 154 Description:
 155                 The directory /sys/devices/system/cpu/cpuX/cpuidle contains per
 156                 logical CPU specific cpuidle information for each online cpu X.
 157                 The processor idle states which are available for use have the
 158                 following attributes:
 159
 160                 name: (RO) Name of the idle state (string).
 161
 162                 latency: (RO) The latency to exit out of this idle state (in
 163                 microseconds).
 164
 165                 power: (RO) The power consumed while in this idle state (in
 166                 milliwatts).
 167
 168                 time: (RO) The total time spent in this idle state (in microseconds).
 169
 170                 usage: (RO) Number of times this state was entered (a count).
 171
 172                 above: (RO) Number of times this state was entered, but the
 173                        observed CPU idle duration was too short for it (a count).
 174
 175                 below: (RO) Number of times this state was entered, but the
 176                        observed CPU idle duration was too long for it (a count).
 177
 178 What:           /sys/devices/system/cpu/cpuX/cpuidle/stateN/desc
 179 Date:           February 2008
 180 KernelVersion:  v2.6.25
 181 Contact:        Linux power management list <linux-pm@vger.kernel.org>
 182 Description:
 183                 (RO) A small description about the idle state (string).
 184
 185
 186 What:           /sys/devices/system/cpu/cpuX/cpuidle/stateN/disable
 187 Date:           March 2012
 188 KernelVersion:  v3.10
 189 Contact:        Linux power management list <linux-pm@vger.kernel.org>
 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/stateN/default_status
 200 Date:           December 2019
 201 KernelVersion:  v5.6
 202 Contact:        Linux power management list <linux-pm@vger.kernel.org>
 203 Description:
 204                 (RO) The default status of this state, "enabled" or "disabled".
 205
 206 What:           /sys/devices/system/cpu/cpuX/cpuidle/stateN/residency
 207 Date:           March 2014
 208 KernelVersion:  v3.15
 209 Contact:        Linux power management list <linux-pm@vger.kernel.org>
 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/stateN/s2idle/
 216 Date:           March 2018
 217 KernelVersion:  v4.17
 218 Contact:        Linux power management list <linux-pm@vger.kernel.org>
 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/stateN/s2idle/time
 226 Date:           March 2018
 227 KernelVersion:  v4.17
 228 Contact:        Linux power management list <linux-pm@vger.kernel.org>
 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/stateN/s2idle/usage
 234 Date:           March 2018
 235 KernelVersion:  v4.17
 236 Contact:        Linux power management list <linux-pm@vger.kernel.org>
 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/cpu#/cpufreq/*
 242 Date:           pre-git history
 243 Contact:        linux-pm@vger.kernel.org
 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/cpu#/cpufreq/freqdomain_cpus
 257 Date:           June 2013
 258 Contact:        linux-pm@vger.kernel.org
 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 driver is in use.
 269
 270
 271 What:           /sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
 272 Date:           August 2008
 273 KernelVersion:  2.6.27
 274 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 275 Description:    Disable L3 cache indices
 276
 277                 These files exist in every CPU's cache/index3 directory. Each
 278                 cache_disable_{0,1} file corresponds to one disable slot which
 279                 can be used to disable a cache index. Reading from these files
 280                 on a processor with this functionality will return the currently
 281                 disabled index for that node. There is one L3 structure per
 282                 node, or per internal node on MCM machines. Writing a valid
 283                 index to one of these files will cause the specificed cache
 284                 index to be disabled.
 285
 286                 All AMD processors with L3 caches provide this functionality.
 287                 For details, see BKDGs at
 288                 http://developer.amd.com/documentation/guides/Pages/default.aspx
 289
 290
 291 What:           /sys/devices/system/cpu/cpufreq/boost
 292 Date:           August 2012
 293 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 294 Description:    Processor frequency boosting control
 295
 296                 This switch controls the boost setting for the whole system.
 297                 Boosting allows the CPU and the firmware to run at a frequency
 298                 beyound it's nominal limit.
 299                 More details can be found in
 300                 Documentation/admin-guide/pm/cpufreq.rst
 301
 302
 303 What:           /sys/devices/system/cpu/cpu#/crash_notes
 304                 /sys/devices/system/cpu/cpu#/crash_notes_size
 305 Date:           April 2013
 306 Contact:        kexec@lists.infradead.org
 307 Description:    address and size of the percpu note.
 308
 309                 crash_notes: the physical address of the memory that holds the
 310                 note of cpu#.
 311
 312                 crash_notes_size: size of the note of cpu#.
 313
 314
 315 What:           /sys/devices/system/cpu/intel_pstate/max_perf_pct
 316                 /sys/devices/system/cpu/intel_pstate/min_perf_pct
 317                 /sys/devices/system/cpu/intel_pstate/no_turbo
 318 Date:           February 2013
 319 Contact:        linux-pm@vger.kernel.org
 320 Description:    Parameters for the Intel P-state driver
 321
 322                 Logic for selecting the current P-state in Intel
 323                 Sandybridge+ processors. The three knobs control
 324                 limits for the P-state that will be requested by the
 325                 driver.
 326
 327                 max_perf_pct: limits the maximum P state that will be requested by
 328                 the driver stated as a percentage of the available performance.
 329
 330                 min_perf_pct: limits the minimum P state that will be requested by
 331                 the driver stated as a percentage of the available performance.
 332
 333                 no_turbo: limits the driver to selecting P states below the turbo
 334                 frequency range.
 335
 336                 More details can be found in
 337                 Documentation/admin-guide/pm/intel_pstate.rst
 338
 339 What:           /sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below>
 340 Date:           July 2014(documented, existed before August 2008)
 341 Contact:        Sudeep Holla <sudeep.holla@arm.com>
 342                 Linux kernel mailing list <linux-kernel@vger.kernel.org>
 343 Description:    Parameters for the CPU cache attributes
 344
 345                 allocation_policy:
 346                         - WriteAllocate: allocate a memory location to a cache line
 347                                          on a cache miss because of a write
 348                         - ReadAllocate: allocate a memory location to a cache line
 349                                         on a cache miss because of a read
 350                         - ReadWriteAllocate: both writeallocate and readallocate
 351
 352                 attributes: LEGACY used only on IA64 and is same as write_policy
 353
 354                 coherency_line_size: the minimum amount of data in bytes that gets
 355                                      transferred from memory to cache
 356
 357                 level: the cache hierarchy in the multi-level cache configuration
 358
 359                 number_of_sets: total number of sets in the cache, a set is a
 360                                 collection of cache lines with the same cache index
 361
 362                 physical_line_partition: number of physical cache line per cache tag
 363
 364                 shared_cpu_list: the list of logical cpus sharing the cache
 365
 366                 shared_cpu_map: logical cpu mask containing the list of cpus sharing
 367                                 the cache
 368
 369                 size: the total cache size in kB
 370
 371                 type:
 372                         - Instruction: cache that only holds instructions
 373                         - Data: cache that only caches data
 374                         - Unified: cache that holds both data and instructions
 375
 376                 ways_of_associativity: degree of freedom in placing a particular block
 377                                         of memory in the cache
 378
 379                 write_policy:
 380                         - WriteThrough: data is written to both the cache line
 381                                         and to the block in the lower-level memory
 382                         - WriteBack: data is written only to the cache line and
 383                                      the modified cache line is written to main
 384                                      memory only when it is replaced
 385
 386
 387 What:           /sys/devices/system/cpu/cpu*/cache/index*/id
 388 Date:           September 2016
 389 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 390 Description:    Cache id
 391
 392                 The id provides a unique number for a specific instance of
 393                 a cache of a particular type. E.g. there may be a level
 394                 3 unified cache on each socket in a server and we may
 395                 assign them ids 0, 1, 2, ...
 396
 397                 Note that id value can be non-contiguous. E.g. level 1
 398                 caches typically exist per core, but there may not be a
 399                 power of two cores on a socket, so these caches may be
 400                 numbered 0, 1, 2, 3, 4, 5, 8, 9, 10, ...
 401
 402 What:           /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats
 403                 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/turbo_stat
 404                 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/sub_turbo_stat
 405                 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/unthrottle
 406                 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/powercap
 407                 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overtemp
 408                 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/supply_fault
 409                 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overcurrent
 410                 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/occ_reset
 411 Date:           March 2016
 412 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 413                 Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
 414 Description:    POWERNV CPUFreq driver's frequency throttle stats directory and
 415                 attributes
 416
 417                 'cpuX/cpufreq/throttle_stats' directory contains the CPU frequency
 418                 throttle stat attributes for the chip. The throttle stats of a cpu
 419                 is common across all the cpus belonging to a chip. Below are the
 420                 throttle attributes exported in the 'throttle_stats' directory:
 421
 422                 - turbo_stat : This file gives the total number of times the max
 423                 frequency is throttled to lower frequency in turbo (at and above
 424                 nominal frequency) range of frequencies.
 425
 426                 - sub_turbo_stat : This file gives the total number of times the
 427                 max frequency is throttled to lower frequency in sub-turbo(below
 428                 nominal frequency) range of frequencies.
 429
 430                 - unthrottle : This file gives the total number of times the max
 431                 frequency is unthrottled after being throttled.
 432
 433                 - powercap : This file gives the total number of times the max
 434                 frequency is throttled due to 'Power Capping'.
 435
 436                 - overtemp : This file gives the total number of times the max
 437                 frequency is throttled due to 'CPU Over Temperature'.
 438
 439                 - supply_fault : This file gives the total number of times the
 440                 max frequency is throttled due to 'Power Supply Failure'.
 441
 442                 - overcurrent : This file gives the total number of times the
 443                 max frequency is throttled due to 'Overcurrent'.
 444
 445                 - occ_reset : This file gives the total number of times the max
 446                 frequency is throttled due to 'OCC Reset'.
 447
 448                 The sysfs attributes representing different throttle reasons like
 449                 powercap, overtemp, supply_fault, overcurrent and occ_reset map to
 450                 the reasons provided by OCC firmware for throttling the frequency.
 451
 452 What:           /sys/devices/system/cpu/cpufreq/policyX/throttle_stats
 453                 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/turbo_stat
 454                 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/sub_turbo_stat
 455                 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/unthrottle
 456                 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/powercap
 457                 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overtemp
 458                 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/supply_fault
 459                 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overcurrent
 460                 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/occ_reset
 461 Date:           March 2016
 462 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 463                 Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
 464 Description:    POWERNV CPUFreq driver's frequency throttle stats directory and
 465                 attributes
 466
 467                 'policyX/throttle_stats' directory and all the attributes are same as
 468                 the /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats directory and
 469                 attributes which give the frequency throttle information of the chip.
 470
 471 What:           /sys/devices/system/cpu/cpuX/regs/
 472                 /sys/devices/system/cpu/cpuX/regs/identification/
 473                 /sys/devices/system/cpu/cpuX/regs/identification/midr_el1
 474                 /sys/devices/system/cpu/cpuX/regs/identification/revidr_el1
 475 Date:           June 2016
 476 Contact:        Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
 477 Description:    AArch64 CPU registers
 478                 'identification' directory exposes the CPU ID registers for
 479                  identifying model and revision of the CPU.
 480
 481 What:           /sys/devices/system/cpu/cpu#/cpu_capacity
 482 Date:           December 2016
 483 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 484 Description:    information about CPUs heterogeneity.
 485
 486                 cpu_capacity: capacity of cpu#.
 487
 488 What:           /sys/devices/system/cpu/vulnerabilities
 489                 /sys/devices/system/cpu/vulnerabilities/meltdown
 490                 /sys/devices/system/cpu/vulnerabilities/spectre_v1
 491                 /sys/devices/system/cpu/vulnerabilities/spectre_v2
 492                 /sys/devices/system/cpu/vulnerabilities/spec_store_bypass
 493                 /sys/devices/system/cpu/vulnerabilities/l1tf
 494                 /sys/devices/system/cpu/vulnerabilities/mds
 495                 /sys/devices/system/cpu/vulnerabilities/tsx_async_abort
 496                 /sys/devices/system/cpu/vulnerabilities/itlb_multihit
 497 Date:           January 2018
 498 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 499 Description:    Information about CPU vulnerabilities
 500
 501                 The files are named after the code names of CPU
 502                 vulnerabilities. The output of those files reflects the
 503                 state of the CPUs in the system. Possible output values:
 504
 505                 "Not affected"    CPU is not affected by the vulnerability
 506                 "Vulnerable"      CPU is affected and no mitigation in effect
 507                 "Mitigation: $M"  CPU is affected and mitigation $M is in effect
 508
 509                 See also: Documentation/admin-guide/hw-vuln/index.rst
 510
 511 What:           /sys/devices/system/cpu/smt
 512                 /sys/devices/system/cpu/smt/active
 513                 /sys/devices/system/cpu/smt/control
 514 Date:           June 2018
 515 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 516 Description:    Control Symetric Multi Threading (SMT)
 517
 518                 active:  Tells whether SMT is active (enabled and siblings online)
 519
 520                 control: Read/write interface to control SMT. Possible
 521                          values:
 522
 523                          "on"             SMT is enabled
 524                          "off"            SMT is disabled
 525                          "forceoff"       SMT is force disabled. Cannot be changed.
 526                          "notsupported"   SMT is not supported by the CPU
 527                          "notimplemented" SMT runtime toggling is not
 528                                           implemented for the architecture
 529
 530                          If control status is "forceoff" or "notsupported" writes
 531                          are rejected.
 532
 533 What:           /sys/devices/system/cpu/cpu#/power/energy_perf_bias
 534 Date:           March 2019
 535 Contact:        linux-pm@vger.kernel.org
 536 Description:    Intel Energy and Performance Bias Hint (EPB)
 537
 538                 EPB for the given CPU in a sliding scale 0 - 15, where a value
 539                 of 0 corresponds to a hint preference for highest performance
 540                 and a value of 15 corresponds to the maximum energy savings.
 541
 542                 In order to change the EPB value for the CPU, write either
 543                 a number in the 0 - 15 sliding scale above, or one of the
 544                 strings: "performance", "balance-performance", "normal",
 545                 "balance-power", "power" (that represent values reflected by
 546                 their meaning), to this attribute.
 547
 548                 This attribute is present for all online CPUs supporting the
 549                 Intel EPB feature.
 550
 551 What:           /sys/devices/system/cpu/umwait_control
 552                 /sys/devices/system/cpu/umwait_control/enable_c02
 553                 /sys/devices/system/cpu/umwait_control/max_time
 554 Date:           May 2019
 555 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 556 Description:    Umwait control
 557
 558                 enable_c02: Read/write interface to control umwait C0.2 state
 559                         Read returns C0.2 state status:
 560                                 0: C0.2 is disabled
 561                                 1: C0.2 is enabled
 562
 563                         Write 'y' or '1'  or 'on' to enable C0.2 state.
 564                         Write 'n' or '0'  or 'off' to disable C0.2 state.
 565
 566                         The interface is case insensitive.
 567
 568                 max_time: Read/write interface to control umwait maximum time
 569                           in TSC-quanta that the CPU can reside in either C0.1
 570                           or C0.2 state. The time is an unsigned 32-bit number.
 571                           Note that a value of zero means there is no limit.
 572                           Low order two bits must be zero.
 573
 574 What:           /sys/devices/system/cpu/svm
 575 Date:           August 2019
 576 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 577                 Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
 578 Description:    Secure Virtual Machine
 579
 580                 If 1, it means the system is using the Protected Execution
 581                 Facility in POWER9 and newer processors. i.e., it is a Secure
 582                 Virtual Machine.