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. 329 330 331What: /sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1} 332Date: August 2008 333KernelVersion: 2.6.27 334Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 335Description: Disable L3 cache indices 336 337 These files exist in every CPU's cache/index3 directory. Each 338 cache_disable_{0,1} file corresponds to one disable slot which 339 can be used to disable a cache index. Reading from these files 340 on a processor with this functionality will return the currently 341 disabled index for that node. There is one L3 structure per 342 node, or per internal node on MCM machines. Writing a valid 343 index to one of these files will cause the specified cache 344 index to be disabled. 345 346 All AMD processors with L3 caches provide this functionality. 347 For details, see BKDGs at 348 https://www.amd.com/en/support/tech-docs?keyword=bios+kernel 349 350 351What: /sys/devices/system/cpu/cpufreq/boost 352Date: August 2012 353Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 354Description: Processor frequency boosting control 355 356 This switch controls the boost setting for the whole system. 357 Boosting allows the CPU and the firmware to run at a frequency 358 beyond its nominal limit. 359 360 More details can be found in 361 Documentation/admin-guide/pm/cpufreq.rst 362 363 364What: /sys/devices/system/cpu/cpuX/crash_notes 365 /sys/devices/system/cpu/cpuX/crash_notes_size 366Date: April 2013 367Contact: kexec@lists.infradead.org 368Description: address and size of the percpu note. 369 370 crash_notes: the physical address of the memory that holds the 371 note of cpuX. 372 373 crash_notes_size: size of the note of cpuX. 374 375 376What: /sys/devices/system/cpu/intel_pstate/max_perf_pct 377 /sys/devices/system/cpu/intel_pstate/min_perf_pct 378 /sys/devices/system/cpu/intel_pstate/no_turbo 379Date: February 2013 380Contact: linux-pm@vger.kernel.org 381Description: Parameters for the Intel P-state driver 382 383 Logic for selecting the current P-state in Intel 384 Sandybridge+ processors. The three knobs control 385 limits for the P-state that will be requested by the 386 driver. 387 388 max_perf_pct: limits the maximum P state that will be requested by 389 the driver stated as a percentage of the available performance. 390 391 min_perf_pct: limits the minimum P state that will be requested by 392 the driver stated as a percentage of the available performance. 393 394 no_turbo: limits the driver to selecting P states below the turbo 395 frequency range. 396 397 More details can be found in 398 Documentation/admin-guide/pm/intel_pstate.rst 399 400What: /sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below> 401Date: July 2014(documented, existed before August 2008) 402Contact: Sudeep Holla <sudeep.holla@arm.com> 403 Linux kernel mailing list <linux-kernel@vger.kernel.org> 404Description: Parameters for the CPU cache attributes 405 406 allocation_policy: 407 - WriteAllocate: 408 allocate a memory location to a cache line 409 on a cache miss because of a write 410 - ReadAllocate: 411 allocate a memory location to a cache line 412 on a cache miss because of a read 413 - ReadWriteAllocate: 414 both writeallocate and readallocate 415 416 coherency_line_size: 417 the minimum amount of data in bytes that gets 418 transferred from memory to cache 419 420 level: 421 the cache hierarchy in the multi-level cache configuration 422 423 number_of_sets: 424 total number of sets in the cache, a set is a 425 collection of cache lines with the same cache index 426 427 physical_line_partition: 428 number of physical cache line per cache tag 429 430 shared_cpu_list: 431 the list of logical cpus sharing the cache 432 433 shared_cpu_map: 434 logical cpu mask containing the list of cpus sharing 435 the cache 436 437 size: 438 the total cache size in kB 439 440 type: 441 - Instruction: cache that only holds instructions 442 - Data: cache that only caches data 443 - Unified: cache that holds both data and instructions 444 445 ways_of_associativity: 446 degree of freedom in placing a particular block 447 of memory in the cache 448 449 write_policy: 450 - WriteThrough: 451 data is written to both the cache line 452 and to the block in the lower-level memory 453 - WriteBack: 454 data is written only to the cache line and 455 the modified cache line is written to main 456 memory only when it is replaced 457 458 459What: /sys/devices/system/cpu/cpu*/cache/index*/id 460Date: September 2016 461Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 462Description: Cache id 463 464 The id provides a unique number for a specific instance of 465 a cache of a particular type. E.g. there may be a level 466 3 unified cache on each socket in a server and we may 467 assign them ids 0, 1, 2, ... 468 469 Note that id value can be non-contiguous. E.g. level 1 470 caches typically exist per core, but there may not be a 471 power of two cores on a socket, so these caches may be 472 numbered 0, 1, 2, 3, 4, 5, 8, 9, 10, ... 473 474What: /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats 475 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/turbo_stat 476 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/sub_turbo_stat 477 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/unthrottle 478 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/powercap 479 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overtemp 480 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/supply_fault 481 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overcurrent 482 /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/occ_reset 483Date: March 2016 484Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 485 Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 486Description: POWERNV CPUFreq driver's frequency throttle stats directory and 487 attributes 488 489 'cpuX/cpufreq/throttle_stats' directory contains the CPU frequency 490 throttle stat attributes for the chip. The throttle stats of a cpu 491 is common across all the cpus belonging to a chip. Below are the 492 throttle attributes exported in the 'throttle_stats' directory: 493 494 - turbo_stat : This file gives the total number of times the max 495 frequency is throttled to lower frequency in turbo (at and above 496 nominal frequency) range of frequencies. 497 498 - sub_turbo_stat : This file gives the total number of times the 499 max frequency is throttled to lower frequency in sub-turbo(below 500 nominal frequency) range of frequencies. 501 502 - unthrottle : This file gives the total number of times the max 503 frequency is unthrottled after being throttled. 504 505 - powercap : This file gives the total number of times the max 506 frequency is throttled due to 'Power Capping'. 507 508 - overtemp : This file gives the total number of times the max 509 frequency is throttled due to 'CPU Over Temperature'. 510 511 - supply_fault : This file gives the total number of times the 512 max frequency is throttled due to 'Power Supply Failure'. 513 514 - overcurrent : This file gives the total number of times the 515 max frequency is throttled due to 'Overcurrent'. 516 517 - occ_reset : This file gives the total number of times the max 518 frequency is throttled due to 'OCC Reset'. 519 520 The sysfs attributes representing different throttle reasons like 521 powercap, overtemp, supply_fault, overcurrent and occ_reset map to 522 the reasons provided by OCC firmware for throttling the frequency. 523 524What: /sys/devices/system/cpu/cpufreq/policyX/throttle_stats 525 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/turbo_stat 526 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/sub_turbo_stat 527 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/unthrottle 528 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/powercap 529 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overtemp 530 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/supply_fault 531 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overcurrent 532 /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/occ_reset 533Date: March 2016 534Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 535 Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 536Description: POWERNV CPUFreq driver's frequency throttle stats directory and 537 attributes 538 539 'policyX/throttle_stats' directory and all the attributes are same as 540 the /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats directory and 541 attributes which give the frequency throttle information of the chip. 542 543What: /sys/devices/system/cpu/cpuX/regs/ 544 /sys/devices/system/cpu/cpuX/regs/identification/ 545 /sys/devices/system/cpu/cpuX/regs/identification/midr_el1 546 /sys/devices/system/cpu/cpuX/regs/identification/revidr_el1 547 /sys/devices/system/cpu/cpuX/regs/identification/aidr_el1 548 /sys/devices/system/cpu/cpuX/regs/identification/smidr_el1 549Date: June 2016 550Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org> 551Description: AArch64 CPU registers 552 553 'identification' directory exposes the CPU ID registers for 554 identifying model and revision of the CPU and SMCU. 555 556What: /sys/devices/system/cpu/aarch32_el0 557Date: May 2021 558Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org> 559Description: Identifies the subset of CPUs in the system that can execute 560 AArch32 (32-bit ARM) applications. If present, the same format as 561 /sys/devices/system/cpu/{offline,online,possible,present} is used. 562 If absent, then all or none of the CPUs can execute AArch32 563 applications and execve() will behave accordingly. 564 565What: /sys/devices/system/cpu/cpuX/cpu_capacity 566Date: December 2016 567Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 568Description: information about CPUs heterogeneity. 569 570 cpu_capacity: capacity of cpuX. 571 572What: /sys/devices/system/cpu/vulnerabilities 573 /sys/devices/system/cpu/vulnerabilities/gather_data_sampling 574 /sys/devices/system/cpu/vulnerabilities/indirect_target_selection 575 /sys/devices/system/cpu/vulnerabilities/itlb_multihit 576 /sys/devices/system/cpu/vulnerabilities/l1tf 577 /sys/devices/system/cpu/vulnerabilities/mds 578 /sys/devices/system/cpu/vulnerabilities/meltdown 579 /sys/devices/system/cpu/vulnerabilities/mmio_stale_data 580 /sys/devices/system/cpu/vulnerabilities/old_microcode 581 /sys/devices/system/cpu/vulnerabilities/reg_file_data_sampling 582 /sys/devices/system/cpu/vulnerabilities/retbleed 583 /sys/devices/system/cpu/vulnerabilities/spec_store_bypass 584 /sys/devices/system/cpu/vulnerabilities/spectre_v1 585 /sys/devices/system/cpu/vulnerabilities/spectre_v2 586 /sys/devices/system/cpu/vulnerabilities/srbds 587 /sys/devices/system/cpu/vulnerabilities/tsa 588 /sys/devices/system/cpu/vulnerabilities/tsx_async_abort 589Date: January 2018 590Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 591Description: Information about CPU vulnerabilities 592 593 The files are named after the code names of CPU 594 vulnerabilities. The output of those files reflects the 595 state of the CPUs in the system. Possible output values: 596 597 ================ ============================================== 598 "Not affected" CPU is not affected by the vulnerability 599 "Vulnerable" CPU is affected and no mitigation in effect 600 "Mitigation: $M" CPU is affected and mitigation $M is in effect 601 ================ ============================================== 602 603 See also: Documentation/admin-guide/hw-vuln/index.rst 604 605What: /sys/devices/system/cpu/smt 606 /sys/devices/system/cpu/smt/active 607 /sys/devices/system/cpu/smt/control 608Date: June 2018 609Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 610Description: Control Symmetric Multi Threading (SMT) 611 612 active: Tells whether SMT is active (enabled and siblings online) 613 614 control: Read/write interface to control SMT. Possible 615 values: 616 617 ================ ========================================= 618 "on" SMT is enabled 619 "off" SMT is disabled 620 "<N>" SMT is enabled with N threads per core. 621 "forceoff" SMT is force disabled. Cannot be changed. 622 "notsupported" SMT is not supported by the CPU 623 "notimplemented" SMT runtime toggling is not 624 implemented for the architecture 625 ================ ========================================= 626 627 If control status is "forceoff" or "notsupported" writes 628 are rejected. Note that enabling SMT on PowerPC skips 629 offline cores. 630 631What: /sys/devices/system/cpu/cpuX/power/energy_perf_bias 632Date: March 2019 633Contact: linux-pm@vger.kernel.org 634Description: Intel Energy and Performance Bias Hint (EPB) 635 636 EPB for the given CPU in a sliding scale 0 - 15, where a value 637 of 0 corresponds to a hint preference for highest performance 638 and a value of 15 corresponds to the maximum energy savings. 639 640 In order to change the EPB value for the CPU, write either 641 a number in the 0 - 15 sliding scale above, or one of the 642 strings: "performance", "balance-performance", "normal", 643 "balance-power", "power" (that represent values reflected by 644 their meaning), to this attribute. 645 646 This attribute is present for all online CPUs supporting the 647 Intel EPB feature. 648 649What: /sys/devices/system/cpu/umwait_control 650 /sys/devices/system/cpu/umwait_control/enable_c02 651 /sys/devices/system/cpu/umwait_control/max_time 652Date: May 2019 653Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 654Description: Umwait control 655 656 enable_c02: Read/write interface to control umwait C0.2 state 657 Read returns C0.2 state status: 658 0: C0.2 is disabled 659 1: C0.2 is enabled 660 661 Write 'y' or '1' or 'on' to enable C0.2 state. 662 Write 'n' or '0' or 'off' to disable C0.2 state. 663 664 The interface is case insensitive. 665 666 max_time: Read/write interface to control umwait maximum time 667 in TSC-quanta that the CPU can reside in either C0.1 668 or C0.2 state. The time is an unsigned 32-bit number. 669 Note that a value of zero means there is no limit. 670 Low order two bits must be zero. 671 672What: /sys/devices/system/cpu/sev 673 /sys/devices/system/cpu/sev/vmpl 674Date: May 2024 675Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 676Description: Secure Encrypted Virtualization (SEV) information 677 678 This directory is only present when running as an SEV-SNP guest. 679 680 vmpl: Reports the Virtual Machine Privilege Level (VMPL) at which 681 the SEV-SNP guest is running. 682 683 684What: /sys/devices/system/cpu/svm 685Date: August 2019 686Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 687 Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 688Description: Secure Virtual Machine 689 690 If 1, it means the system is using the Protected Execution 691 Facility in POWER9 and newer processors. i.e., it is a Secure 692 Virtual Machine. 693 694What: /sys/devices/system/cpu/cpuX/purr 695Date: Apr 2005 696Contact: Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 697Description: PURR ticks for this CPU since the system boot. 698 699 The Processor Utilization Resources Register (PURR) is 700 a 64-bit counter which provides an estimate of the 701 resources used by the CPU thread. The contents of this 702 register increases monotonically. This sysfs interface 703 exposes the number of PURR ticks for cpuX. 704 705What: /sys/devices/system/cpu/cpuX/spurr 706Date: Dec 2006 707Contact: Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 708Description: SPURR ticks for this CPU since the system boot. 709 710 The Scaled Processor Utilization Resources Register 711 (SPURR) is a 64-bit counter that provides a frequency 712 invariant estimate of the resources used by the CPU 713 thread. The contents of this register increases 714 monotonically. This sysfs interface exposes the number 715 of SPURR ticks for cpuX. 716 717What: /sys/devices/system/cpu/cpuX/idle_purr 718Date: Apr 2020 719Contact: Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 720Description: PURR ticks for cpuX when it was idle. 721 722 This sysfs interface exposes the number of PURR ticks 723 for cpuX when it was idle. 724 725What: /sys/devices/system/cpu/cpuX/idle_spurr 726Date: Apr 2020 727Contact: Linux for PowerPC mailing list <linuxppc-dev@lists.ozlabs.org> 728Description: SPURR ticks for cpuX when it was idle. 729 730 This sysfs interface exposes the number of SPURR ticks 731 for cpuX when it was idle. 732 733What: /sys/devices/system/cpu/cpuX/mte_tcf_preferred 734Date: July 2021 735Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org> 736Description: Preferred MTE tag checking mode 737 738 When a user program specifies more than one MTE tag checking 739 mode, this sysfs node is used to specify which mode should 740 be preferred when scheduling a task on that CPU. Possible 741 values: 742 743 ================ ============================================== 744 "sync" Prefer synchronous mode 745 "asymm" Prefer asymmetric mode 746 "async" Prefer asynchronous mode 747 ================ ============================================== 748 749 See also: Documentation/arch/arm64/memory-tagging-extension.rst 750 751What: /sys/devices/system/cpu/nohz_full 752Date: Apr 2015 753Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 754Description: 755 (RO) the list of CPUs that are in nohz_full mode. 756 These CPUs are set by boot parameter "nohz_full=". 757 758What: /sys/devices/system/cpu/isolated 759Date: Apr 2015 760Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 761Description: 762 (RO) the list of CPUs that are isolated and don't 763 participate in load balancing. These CPUs are set by 764 boot parameter "isolcpus=". 765 766What: /sys/devices/system/cpu/crash_hotplug 767Date: Aug 2023 768Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 769Description: 770 (RO) indicates whether or not the kernel updates relevant kexec 771 segments on memory hot un/plug and/or on/offline events, avoiding the 772 need to reload kdump kernel. 773 774What: /sys/devices/system/cpu/enabled 775Date: Nov 2022 776Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> 777Description: 778 (RO) the list of CPUs that can be brought online. 779