1What: /sys/devices/system/cpu/ 2Date: pre-git history 3Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 4Description: 5 A collection of both global and individual CPU attributes 6 7 Individual CPU attributes are contained in subdirectories 8 named by the kernel's logical CPU number, e.g.: 9 10 /sys/devices/system/cpu/cpuX/ 11 12What: /sys/devices/system/cpu/kernel_max 13 /sys/devices/system/cpu/offline 14 /sys/devices/system/cpu/online 15 /sys/devices/system/cpu/possible 16 /sys/devices/system/cpu/present 17Date: December 2008 18Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 19Description: CPU topology files that describe kernel limits related to 20 hotplug. Briefly: 21 22 kernel_max: the maximum cpu index allowed by the kernel 23 configuration. 24 25 offline: cpus that are not online because they have been 26 HOTPLUGGED off or exceed the limit of cpus allowed by the 27 kernel configuration (kernel_max above). 28 29 online: cpus that are online and being scheduled. 30 31 possible: cpus that have been allocated resources and can be 32 brought online if they are present. 33 34 present: cpus that have been identified as being present in 35 the system. 36 37 See Documentation/admin-guide/cputopology.rst for more information. 38 39 40What: /sys/devices/system/cpu/probe 41 /sys/devices/system/cpu/release 42Date: November 2009 43Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 44Description: Dynamic addition and removal of CPU's. This is not hotplug 45 removal, this is meant complete removal/addition of the CPU 46 from the system. 47 48 probe: writes to this file will dynamically add a CPU to the 49 system. Information written to the file to add CPU's is 50 architecture specific. 51 52 release: writes to this file dynamically remove a CPU from 53 the system. Information written to the file to remove CPU's 54 is architecture specific. 55 56What: /sys/devices/system/cpu/cpuX/node 57Date: October 2009 58Contact: Linux memory management mailing list <linux-mm@kvack.org> 59Description: Discover NUMA node a CPU belongs to 60 61 When CONFIG_NUMA is enabled, a symbolic link that points 62 to the corresponding NUMA node directory. 63 64 For example, the following symlink is created for cpu42 65 in NUMA node 2: 66 67 /sys/devices/system/cpu/cpu42/node2 -> ../../node/node2 68 69 70What: /sys/devices/system/cpu/cpuX/topology/core_siblings 71 /sys/devices/system/cpu/cpuX/topology/core_siblings_list 72 /sys/devices/system/cpu/cpuX/topology/physical_package_id 73 /sys/devices/system/cpu/cpuX/topology/thread_siblings 74 /sys/devices/system/cpu/cpuX/topology/thread_siblings_list 75 /sys/devices/system/cpu/cpuX/topology/ppin 76Date: December 2008 77Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 78Description: CPU topology files that describe a logical CPU's relationship 79 to other cores and threads in the same physical package. 80 81 One cpuX directory is created per logical CPU in the system, 82 e.g. /sys/devices/system/cpu/cpu42/. 83 84 Briefly, the files above are: 85 86 core_siblings: internal kernel map of cpuX's hardware threads 87 within the same physical_package_id. 88 89 core_siblings_list: human-readable list of the logical CPU 90 numbers within the same physical_package_id as cpuX. 91 92 physical_package_id: physical package id of cpuX. Typically 93 corresponds to a physical socket number, but the actual value 94 is architecture and platform dependent. 95 96 thread_siblings: internal kernel map of cpuX's hardware 97 threads within the same core as cpuX 98 99 thread_siblings_list: human-readable list of cpuX's hardware 100 threads within the same core as cpuX 101 102 ppin: human-readable Protected Processor Identification 103 Number of the socket the cpu# belongs to. There should be 104 one per physical_package_id. File is readable only to 105 admin. 106 107 See Documentation/admin-guide/cputopology.rst for more information. 108 109 110What: /sys/devices/system/cpu/cpuidle/available_governors 111 /sys/devices/system/cpu/cpuidle/current_driver 112 /sys/devices/system/cpu/cpuidle/current_governor 113 /sys/devices/system/cpu/cpuidle/current_governer_ro 114 /sys/devices/system/cpu/cpuidle/intel_c1_demotion 115Date: September 2007 116Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 117Description: Discover cpuidle policy and mechanism 118 119 Various CPUs today support multiple idle levels that are 120 differentiated by varying exit latencies and power 121 consumption during idle. 122 123 Idle policy (governor) is differentiated from idle mechanism 124 (driver). 125 126 available_governors: (RO) displays a space separated list of 127 available governors. 128 129 current_driver: (RO) displays current idle mechanism. 130 131 current_governor: (RW) displays current idle policy. Users can 132 switch the governor at runtime by writing to this file. 133 134 current_governor_ro: (RO) displays current idle policy. 135 136 intel_c1_demotion: (RW) enables/disables the C1 demotion 137 feature on Intel CPUs. 138 139 See Documentation/admin-guide/pm/cpuidle.rst, 140 Documentation/admin-guide/pm/intel_idle.rst, and 141 Documentation/driver-api/pm/cpuidle.rst for more information. 142 143 144What: /sys/devices/system/cpu/cpuX/cpuidle/state<N>/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 151Date: September 2007 152KernelVersion: v2.6.24 153Contact: Linux power management list <linux-pm@vger.kernel.org> 154Description: 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 ======== ==== ================================================= 161 name: (RO) Name of the idle state (string). 162 163 latency: (RO) The latency to exit out of this idle state (in 164 microseconds). 165 166 power: (RO) The power consumed while in this idle state (in 167 milliwatts). 168 169 time: (RO) The total time spent in this idle state 170 (in microseconds). 171 172 usage: (RO) Number of times this state was entered (a count). 173 174 above: (RO) Number of times this state was entered, but the 175 observed CPU idle duration was too short for it 176 (a count). 177 178 below: (RO) Number of times this state was entered, but the 179 observed CPU idle duration was too long for it 180 (a count). 181 ======== ==== ================================================= 182 183What: /sys/devices/system/cpu/cpuX/cpuidle/state<N>/desc 184Date: February 2008 185KernelVersion: v2.6.25 186Contact: Linux power management list <linux-pm@vger.kernel.org> 187Description: 188 (RO) A small description about the idle state (string). 189 190 191What: /sys/devices/system/cpu/cpuX/cpuidle/state<N>/disable 192Date: March 2012 193KernelVersion: v3.10 194Contact: Linux power management list <linux-pm@vger.kernel.org> 195Description: 196 (RW) Option to disable this idle state (bool). The behavior and 197 the effect of the disable variable depends on the implementation 198 of a particular governor. In the ladder governor, for example, 199 it is not coherent, i.e. if one is disabling a light state, then 200 all deeper states are disabled as well, but the disable variable 201 does not reflect it. Likewise, if one enables a deep state but a 202 lighter state still is disabled, then this has no effect. 203 204What: /sys/devices/system/cpu/cpuX/cpuidle/state<N>/default_status 205Date: December 2019 206KernelVersion: v5.6 207Contact: Linux power management list <linux-pm@vger.kernel.org> 208Description: 209 (RO) The default status of this state, "enabled" or "disabled". 210 211What: /sys/devices/system/cpu/cpuX/cpuidle/state<N>/residency 212Date: March 2014 213KernelVersion: v3.15 214Contact: Linux power management list <linux-pm@vger.kernel.org> 215Description: 216 (RO) Display the target residency i.e. the minimum amount of 217 time (in microseconds) this cpu should spend in this idle state 218 to make the transition worth the effort. 219 220What: /sys/devices/system/cpu/cpuX/cpuidle/state<N>/s2idle/ 221Date: March 2018 222KernelVersion: v4.17 223Contact: Linux power management list <linux-pm@vger.kernel.org> 224Description: 225 Idle state usage statistics related to suspend-to-idle. 226 227 This attribute group is only present for states that can be 228 used in suspend-to-idle with suspended timekeeping. 229 230What: /sys/devices/system/cpu/cpuX/cpuidle/state<N>/s2idle/time 231Date: March 2018 232KernelVersion: v4.17 233Contact: Linux power management list <linux-pm@vger.kernel.org> 234Description: 235 Total time spent by the CPU in suspend-to-idle (with scheduler 236 tick suspended) after requesting this state. 237 238What: /sys/devices/system/cpu/cpuX/cpuidle/state<N>/s2idle/usage 239Date: March 2018 240KernelVersion: v4.17 241Contact: Linux power management list <linux-pm@vger.kernel.org> 242Description: 243 Total number of times this state has been requested by the CPU 244 while entering suspend-to-idle. 245 246What: /sys/devices/system/cpu/cpuX/cpufreq/* 247Date: pre-git history 248Contact: linux-pm@vger.kernel.org 249Description: Discover and change clock speed of CPUs 250 251 Clock scaling allows you to change the clock speed of the 252 CPUs on the fly. This is a nice method to save battery 253 power, because the lower the clock speed, the less power 254 the CPU consumes. 255 256 There are many knobs to tweak in this directory. 257 258 See files in Documentation/cpu-freq/ for more information. 259 260 261What: /sys/devices/system/cpu/cpuX/cpufreq/freqdomain_cpus 262Date: June 2013 263Contact: linux-pm@vger.kernel.org 264Description: Discover CPUs in the same CPU frequency coordination domain 265 266 freqdomain_cpus is the list of CPUs (online+offline) that share 267 the same clock/freq domain (possibly at the hardware level). 268 That information may be hidden from the cpufreq core and the 269 value of related_cpus may be different from freqdomain_cpus. This 270 attribute is useful for user space DVFS controllers to get better 271 power/performance results for platforms using acpi-cpufreq. 272 273 This file is only present if the acpi-cpufreq or the cppc-cpufreq 274 drivers are in use. 275 276What: /sys/devices/system/cpu/cpuX/cpufreq/auto_select 277Date: May 2025 278Contact: linux-pm@vger.kernel.org 279Description: Autonomous selection enable 280 281 Read/write interface to control autonomous selection enable 282 Read returns autonomous selection status: 283 0: autonomous selection is disabled 284 1: autonomous selection is enabled 285 286 Write 'y' or '1' or 'on' to enable autonomous selection. 287 Write 'n' or '0' or 'off' to disable autonomous selection. 288 289 This file is only present if the cppc-cpufreq driver is in use. 290 291What: /sys/devices/system/cpu/cpuX/cpufreq/auto_act_window 292Date: May 2025 293Contact: linux-pm@vger.kernel.org 294Description: Autonomous activity window 295 296 This file indicates a moving utilization sensitivity window to 297 the platform's autonomous selection policy. 298 299 Read/write an integer represents autonomous activity window (in 300 microseconds) from/to this file. The max value to write is 301 1270000000 but the max significand is 127. This means that if 128 302 is written to this file, 127 will be stored. If the value is 303 greater than 130, only the first two digits will be saved as 304 significand. 305 306 Writing a zero value to this file enable the platform to 307 determine an appropriate Activity Window depending on the workload. 308 309 Writing to this file only has meaning when Autonomous Selection is 310 enabled. 311 312 This file is only present if the cppc-cpufreq driver is in use. 313 314What: /sys/devices/system/cpu/cpuX/cpufreq/energy_performance_preference_val 315Date: May 2025 316Contact: linux-pm@vger.kernel.org 317Description: Energy performance preference 318 319 Read/write an 8-bit integer from/to this file. This file 320 represents a range of values from 0 (performance preference) to 321 0xFF (energy efficiency preference) that influences the rate of 322 performance increase/decrease and the result of the hardware's 323 energy efficiency and performance optimization policies. 324 325 Writing to this file only has meaning when Autonomous Selection is 326 enabled. 327 328 This file is only present if the cppc-cpufreq driver is in use. 329 330What: /sys/devices/system/cpu/cpuX/cpufreq/perf_limited 331Date: February 2026 332Contact: linux-pm@vger.kernel.org 333Description: Performance Limited 334 335 Read to check if platform throttling (thermal/power/current 336 limits) caused delivered performance to fall below the 337 requested level. A non-zero value indicates throttling occurred. 338 339 Write the bitmask of bits to clear: 340 341 - 0x1 = clear bit 0 (desired performance excursion) 342 - 0x2 = clear bit 1 (minimum performance excursion) 343 - 0x3 = clear both bits 344 345 The platform sets these bits; OSPM can only clear them. 346 347 This file is only present if the cppc-cpufreq driver is in use. 348 349What: /sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1} 350Date: August 2008 351KernelVersion: 2.6.27 352Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 353Description: Disable L3 cache indices 354 355 These files exist in every CPU's cache/index3 directory. Each 356 cache_disable_{0,1} file corresponds to one disable slot which 357 can be used to disable a cache index. Reading from these files 358 on a processor with this functionality will return the currently 359 disabled index for that node. There is one L3 structure per 360 node, or per internal node on MCM machines. Writing a valid 361 index to one of these files will cause the specified cache 362 index to be disabled. 363 364 All AMD processors with L3 caches provide this functionality. 365 For details, see BKDGs at 366 https://www.amd.com/en/support/tech-docs?keyword=bios+kernel 367 368 369What: /sys/devices/system/cpu/cpufreq/boost 370Date: August 2012 371Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 372Description: Processor frequency boosting control 373 374 This switch controls the boost setting for the whole system. 375 Boosting allows the CPU and the firmware to run at a frequency 376 beyond its nominal limit. 377 378 More details can be found in 379 Documentation/admin-guide/pm/cpufreq.rst 380 381 382What: /sys/devices/system/cpu/cpuX/crash_notes 383 /sys/devices/system/cpu/cpuX/crash_notes_size 384Date: April 2013 385Contact: kexec@lists.infradead.org 386Description: address and size of the percpu note. 387 388 crash_notes: the physical address of the memory that holds the 389 note of cpuX. 390 391 crash_notes_size: size of the note of cpuX. 392 393 394What: /sys/devices/system/cpu/intel_pstate/max_perf_pct 395 /sys/devices/system/cpu/intel_pstate/min_perf_pct 396 /sys/devices/system/cpu/intel_pstate/no_turbo 397Date: February 2013 398Contact: linux-pm@vger.kernel.org 399Description: Parameters for the Intel P-state driver 400 401 Logic for selecting the current P-state in Intel 402 Sandybridge+ processors. The three knobs control 403 limits for the P-state that will be requested by the 404 driver. 405 406 max_perf_pct: limits the maximum P state that will be requested by 407 the driver stated as a percentage of the available performance. 408 409 min_perf_pct: limits the minimum P state that will be requested by 410 the driver stated as a percentage of the available performance. 411 412 no_turbo: limits the driver to selecting P states below the turbo 413 frequency range. 414 415 More details can be found in 416 Documentation/admin-guide/pm/intel_pstate.rst 417 418What: /sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below> 419Date: July 2014(documented, existed before August 2008) 420Contact: Sudeep Holla <sudeep.holla@arm.com> 421 Linux kernel mailing list <linux-kernel@vger.kernel.org> 422Description: Parameters for the CPU cache attributes 423 424 allocation_policy: 425 - WriteAllocate: 426 allocate a memory location to a cache line 427 on a cache miss because of a write 428 - ReadAllocate: 429 allocate a memory location to a cache line 430 on a cache miss because of a read 431 - ReadWriteAllocate: 432 both writeallocate and readallocate 433 434 coherency_line_size: 435 the minimum amount of data in bytes that gets 436 transferred from memory to cache 437 438 level: 439 the cache hierarchy in the multi-level cache configuration 440 441 number_of_sets: 442 total number of sets in the cache, a set is a 443 collection of cache lines with the same cache index 444 445 physical_line_partition: 446 number of physical cache line per cache tag 447 448 shared_cpu_list: 449 the list of logical cpus sharing the cache 450 451 shared_cpu_map: 452 logical cpu mask containing the list of cpus sharing 453 the cache 454 455 size: 456 the total cache size in kB 457 458 type: 459 - Instruction: cache that only holds instructions 460 - Data: cache that only caches data 461 - Unified: cache that holds both data and instructions 462 463 ways_of_associativity: 464 degree of freedom in placing a particular block 465 of memory in the cache 466 467 write_policy: 468 - WriteThrough: 469 data is written to both the cache line 470 and to the block in the lower-level memory 471 - WriteBack: 472 data is written only to the cache line and 473 the modified cache line is written to main 474 memory only when it is replaced 475 476 477What: /sys/devices/system/cpu/cpu*/cache/index*/id 478Date: September 2016 479Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 480Description: Cache id 481 482 The id provides a unique number for a specific instance of 483 a cache of a particular type. E.g. there may be a level 484 3 unified cache on each socket in a server and we may 485 assign them ids 0, 1, 2, ... 486 487 Note that id value can be non-contiguous. E.g. level 1 488 caches typically exist per core, but there may not be a 489 power of two cores on a socket, so these caches may be 490 numbered 0, 1, 2, 3, 4, 5, 8, 9, 10, ... 491 492What: /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats 493 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/turbo_stat 494 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/sub_turbo_stat 495 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/unthrottle 496 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/powercap 497 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overtemp 498 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/supply_fault 499 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overcurrent 500 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/occ_reset 501Date: March 2016 502Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 503 Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 504Description: POWERNV CPUFreq driver's frequency throttle stats directory and 505 attributes 506 507 'cpuX/cpufreq/throttle_stats' directory contains the CPU frequency 508 throttle stat attributes for the chip. The throttle stats of a cpu 509 is common across all the cpus belonging to a chip. Below are the 510 throttle attributes exported in the 'throttle_stats' directory: 511 512 - turbo_stat : This file gives the total number of times the max 513 frequency is throttled to lower frequency in turbo (at and above 514 nominal frequency) range of frequencies. 515 516 - sub_turbo_stat : This file gives the total number of times the 517 max frequency is throttled to lower frequency in sub-turbo(below 518 nominal frequency) range of frequencies. 519 520 - unthrottle : This file gives the total number of times the max 521 frequency is unthrottled after being throttled. 522 523 - powercap : This file gives the total number of times the max 524 frequency is throttled due to 'Power Capping'. 525 526 - overtemp : This file gives the total number of times the max 527 frequency is throttled due to 'CPU Over Temperature'. 528 529 - supply_fault : This file gives the total number of times the 530 max frequency is throttled due to 'Power Supply Failure'. 531 532 - overcurrent : This file gives the total number of times the 533 max frequency is throttled due to 'Overcurrent'. 534 535 - occ_reset : This file gives the total number of times the max 536 frequency is throttled due to 'OCC Reset'. 537 538 The sysfs attributes representing different throttle reasons like 539 powercap, overtemp, supply_fault, overcurrent and occ_reset map to 540 the reasons provided by OCC firmware for throttling the frequency. 541 542What: /sys/devices/system/cpu/cpufreq/policyX/throttle_stats 543 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/turbo_stat 544 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/sub_turbo_stat 545 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/unthrottle 546 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/powercap 547 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overtemp 548 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/supply_fault 549 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overcurrent 550 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/occ_reset 551Date: March 2016 552Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 553 Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 554Description: POWERNV CPUFreq driver's frequency throttle stats directory and 555 attributes 556 557 'policyX/throttle_stats' directory and all the attributes are same as 558 the /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats directory and 559 attributes which give the frequency throttle information of the chip. 560 561What: /sys/devices/system/cpu/cpuX/regs/ 562 /sys/devices/system/cpu/cpuX/regs/identification/ 563 /sys/devices/system/cpu/cpuX/regs/identification/midr_el1 564 /sys/devices/system/cpu/cpuX/regs/identification/revidr_el1 565 /sys/devices/system/cpu/cpuX/regs/identification/aidr_el1 566 /sys/devices/system/cpu/cpuX/regs/identification/smidr_el1 567Date: June 2016 568Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org> 569Description: AArch64 CPU registers 570 571 'identification' directory exposes the CPU ID registers for 572 identifying model and revision of the CPU and SMCU. 573 574What: /sys/devices/system/cpu/aarch32_el0 575Date: May 2021 576Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org> 577Description: Identifies the subset of CPUs in the system that can execute 578 AArch32 (32-bit ARM) applications. If present, the same format as 579 /sys/devices/system/cpu/{offline,online,possible,present} is used. 580 If absent, then all or none of the CPUs can execute AArch32 581 applications and execve() will behave accordingly. 582 583What: /sys/devices/system/cpu/cpuX/cpu_capacity 584Date: December 2016 585Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 586Description: information about CPUs heterogeneity. 587 588 cpu_capacity: capacity of cpuX. 589 590What: /sys/devices/system/cpu/vulnerabilities 591 /sys/devices/system/cpu/vulnerabilities/gather_data_sampling 592 /sys/devices/system/cpu/vulnerabilities/indirect_target_selection 593 /sys/devices/system/cpu/vulnerabilities/itlb_multihit 594 /sys/devices/system/cpu/vulnerabilities/l1tf 595 /sys/devices/system/cpu/vulnerabilities/mds 596 /sys/devices/system/cpu/vulnerabilities/meltdown 597 /sys/devices/system/cpu/vulnerabilities/mmio_stale_data 598 /sys/devices/system/cpu/vulnerabilities/old_microcode 599 /sys/devices/system/cpu/vulnerabilities/reg_file_data_sampling 600 /sys/devices/system/cpu/vulnerabilities/retbleed 601 /sys/devices/system/cpu/vulnerabilities/spec_store_bypass 602 /sys/devices/system/cpu/vulnerabilities/spectre_v1 603 /sys/devices/system/cpu/vulnerabilities/spectre_v2 604 /sys/devices/system/cpu/vulnerabilities/srbds 605 /sys/devices/system/cpu/vulnerabilities/tsa 606 /sys/devices/system/cpu/vulnerabilities/tsx_async_abort 607 /sys/devices/system/cpu/vulnerabilities/vmscape 608Date: January 2018 609Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 610Description: Information about CPU vulnerabilities 611 612 The files are named after the code names of CPU 613 vulnerabilities. The output of those files reflects the 614 state of the CPUs in the system. Possible output values: 615 616 ================ ============================================== 617 "Not affected" CPU is not affected by the vulnerability 618 "Vulnerable" CPU is affected and no mitigation in effect 619 "Mitigation: $M" CPU is affected and mitigation $M is in effect 620 ================ ============================================== 621 622 See also: Documentation/admin-guide/hw-vuln/index.rst 623 624What: /sys/devices/system/cpu/smt 625 /sys/devices/system/cpu/smt/active 626 /sys/devices/system/cpu/smt/control 627Date: June 2018 628Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 629Description: Control Symmetric Multi Threading (SMT) 630 631 active: Tells whether SMT is active (enabled and siblings online) 632 633 control: Read/write interface to control SMT. Possible 634 values: 635 636 ================ ========================================= 637 "on" SMT is enabled 638 "off" SMT is disabled 639 "<N>" SMT is enabled with N threads per core. 640 "forceoff" SMT is force disabled. Cannot be changed. 641 "notsupported" SMT is not supported by the CPU 642 "notimplemented" SMT runtime toggling is not 643 implemented for the architecture 644 ================ ========================================= 645 646 If control status is "forceoff" or "notsupported" writes 647 are rejected. Note that enabling SMT on PowerPC skips 648 offline cores. 649 650What: /sys/devices/system/cpu/cpuX/power/energy_perf_bias 651Date: March 2019 652Contact: linux-pm@vger.kernel.org 653Description: Intel Energy and Performance Bias Hint (EPB) 654 655 EPB for the given CPU in a sliding scale 0 - 15, where a value 656 of 0 corresponds to a hint preference for highest performance 657 and a value of 15 corresponds to the maximum energy savings. 658 659 In order to change the EPB value for the CPU, write either 660 a number in the 0 - 15 sliding scale above, or one of the 661 strings: "performance", "balance-performance", "normal", 662 "balance-power", "power" (that represent values reflected by 663 their meaning), to this attribute. 664 665 This attribute is present for all online CPUs supporting the 666 Intel EPB feature. 667 668What: /sys/devices/system/cpu/umwait_control 669 /sys/devices/system/cpu/umwait_control/enable_c02 670 /sys/devices/system/cpu/umwait_control/max_time 671Date: May 2019 672Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 673Description: Umwait control 674 675 enable_c02: Read/write interface to control umwait C0.2 state 676 Read returns C0.2 state status: 677 0: C0.2 is disabled 678 1: C0.2 is enabled 679 680 Write 'y' or '1' or 'on' to enable C0.2 state. 681 Write 'n' or '0' or 'off' to disable C0.2 state. 682 683 The interface is case insensitive. 684 685 max_time: Read/write interface to control umwait maximum time 686 in TSC-quanta that the CPU can reside in either C0.1 687 or C0.2 state. The time is an unsigned 32-bit number. 688 Note that a value of zero means there is no limit. 689 Low order two bits must be zero. 690 691What: /sys/devices/system/cpu/sev 692 /sys/devices/system/cpu/sev/vmpl 693Date: May 2024 694Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 695Description: Secure Encrypted Virtualization (SEV) information 696 697 This directory is only present when running as an SEV-SNP guest. 698 699 vmpl: Reports the Virtual Machine Privilege Level (VMPL) at which 700 the SEV-SNP guest is running. 701 702 703What: /sys/devices/system/cpu/svm 704Date: August 2019 705Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 706 Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 707Description: Secure Virtual Machine 708 709 If 1, it means the system is using the Protected Execution 710 Facility in POWER9 and newer processors. i.e., it is a Secure 711 Virtual Machine. 712 713What: /sys/devices/system/cpu/cpuX/purr 714Date: Apr 2005 715Contact: Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 716Description: PURR ticks for this CPU since the system boot. 717 718 The Processor Utilization Resources Register (PURR) is 719 a 64-bit counter which provides an estimate of the 720 resources used by the CPU thread. The contents of this 721 register increases monotonically. This sysfs interface 722 exposes the number of PURR ticks for cpuX. 723 724What: /sys/devices/system/cpu/cpuX/spurr 725Date: Dec 2006 726Contact: Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 727Description: SPURR ticks for this CPU since the system boot. 728 729 The Scaled Processor Utilization Resources Register 730 (SPURR) is a 64-bit counter that provides a frequency 731 invariant estimate of the resources used by the CPU 732 thread. The contents of this register increases 733 monotonically. This sysfs interface exposes the number 734 of SPURR ticks for cpuX. 735 736What: /sys/devices/system/cpu/cpuX/idle_purr 737Date: Apr 2020 738Contact: Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 739Description: PURR ticks for cpuX when it was idle. 740 741 This sysfs interface exposes the number of PURR ticks 742 for cpuX when it was idle. 743 744What: /sys/devices/system/cpu/cpuX/idle_spurr 745Date: Apr 2020 746Contact: Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 747Description: SPURR ticks for cpuX when it was idle. 748 749 This sysfs interface exposes the number of SPURR ticks 750 for cpuX when it was idle. 751 752What: /sys/devices/system/cpu/cpuX/mte_tcf_preferred 753Date: July 2021 754Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org> 755Description: Preferred MTE tag checking mode 756 757 When a user program specifies more than one MTE tag checking 758 mode, this sysfs node is used to specify which mode should 759 be preferred when scheduling a task on that CPU. Possible 760 values: 761 762 ================ ============================================== 763 "sync" Prefer synchronous mode 764 "asymm" Prefer asymmetric mode 765 "async" Prefer asynchronous mode 766 ================ ============================================== 767 768 See also: Documentation/arch/arm64/memory-tagging-extension.rst 769 770What: /sys/devices/system/cpu/nohz_full 771Date: Apr 2015 772Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 773Description: 774 (RO) the list of CPUs that are in nohz_full mode. 775 These CPUs are set by boot parameter "nohz_full=". 776 777What: /sys/devices/system/cpu/isolated 778Date: Apr 2015 779Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 780Description: 781 (RO) the list of CPUs that are isolated and don't 782 participate in load balancing. These CPUs are set by 783 boot parameter "isolcpus=". 784 785What: /sys/devices/system/cpu/housekeeping 786Date: Oct 2025 787Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 788Description: 789 (RO) the list of logical CPUs that are designated by the kernel as 790 "housekeeping". Each CPU are responsible for handling essential 791 system-wide background tasks, including RCU callbacks, delayed 792 timer callbacks, and unbound workqueues, minimizing scheduling 793 jitter on low-latency, isolated CPUs. These CPUs are set when boot 794 parameter "isolcpus=nohz" or "nohz_full=" is specified. 795 796What: /sys/devices/system/cpu/crash_hotplug 797Date: Aug 2023 798Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 799Description: 800 (RO) indicates whether or not the kernel updates relevant kexec 801 segments on memory hot un/plug and/or on/offline events, avoiding the 802 need to reload kdump kernel. 803 804What: /sys/devices/system/cpu/enabled 805Date: Nov 2022 806Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 807Description: 808 (RO) the list of CPUs that can be brought online. 809