What: /sys/devices/system/cpu/ Date: pre-git history Contact: Linux kernel mailing list Description: A collection of both global and individual CPU attributes Individual CPU attributes are contained in subdirectories named by the kernel's logical CPU number, e.g.: /sys/devices/system/cpu/cpuX/ What: /sys/devices/system/cpu/kernel_max /sys/devices/system/cpu/offline /sys/devices/system/cpu/online /sys/devices/system/cpu/possible /sys/devices/system/cpu/present Date: December 2008 Contact: Linux kernel mailing list Description: CPU topology files that describe kernel limits related to hotplug. Briefly: kernel_max: the maximum cpu index allowed by the kernel configuration. offline: cpus that are not online because they have been HOTPLUGGED off or exceed the limit of cpus allowed by the kernel configuration (kernel_max above). online: cpus that are online and being scheduled. possible: cpus that have been allocated resources and can be brought online if they are present. present: cpus that have been identified as being present in the system. See Documentation/admin-guide/cputopology.rst for more information. What: /sys/devices/system/cpu/probe /sys/devices/system/cpu/release Date: November 2009 Contact: Linux kernel mailing list Description: Dynamic addition and removal of CPU's. This is not hotplug removal, this is meant complete removal/addition of the CPU from the system. probe: writes to this file will dynamically add a CPU to the system. Information written to the file to add CPU's is architecture specific. release: writes to this file dynamically remove a CPU from the system. Information written to the file to remove CPU's is architecture specific. What: /sys/devices/system/cpu/cpuX/node Date: October 2009 Contact: Linux memory management mailing list Description: Discover NUMA node a CPU belongs to When CONFIG_NUMA is enabled, a symbolic link that points to the corresponding NUMA node directory. For example, the following symlink is created for cpu42 in NUMA node 2: /sys/devices/system/cpu/cpu42/node2 -> ../../node/node2 What: /sys/devices/system/cpu/cpuX/topology/core_siblings /sys/devices/system/cpu/cpuX/topology/core_siblings_list /sys/devices/system/cpu/cpuX/topology/physical_package_id /sys/devices/system/cpu/cpuX/topology/thread_siblings /sys/devices/system/cpu/cpuX/topology/thread_siblings_list /sys/devices/system/cpu/cpuX/topology/ppin Date: December 2008 Contact: Linux kernel mailing list Description: CPU topology files that describe a logical CPU's relationship to other cores and threads in the same physical package. One cpuX directory is created per logical CPU in the system, e.g. /sys/devices/system/cpu/cpu42/. Briefly, the files above are: core_siblings: internal kernel map of cpuX's hardware threads within the same physical_package_id. core_siblings_list: human-readable list of the logical CPU numbers within the same physical_package_id as cpuX. physical_package_id: physical package id of cpuX. Typically corresponds to a physical socket number, but the actual value is architecture and platform dependent. thread_siblings: internal kernel map of cpuX's hardware threads within the same core as cpuX thread_siblings_list: human-readable list of cpuX's hardware threads within the same core as cpuX ppin: human-readable Protected Processor Identification Number of the socket the cpu# belongs to. There should be one per physical_package_id. File is readable only to admin. See Documentation/admin-guide/cputopology.rst for more information. What: /sys/devices/system/cpu/cpuidle/available_governors /sys/devices/system/cpu/cpuidle/current_driver /sys/devices/system/cpu/cpuidle/current_governor /sys/devices/system/cpu/cpuidle/current_governer_ro Date: September 2007 Contact: Linux kernel mailing list Description: Discover cpuidle policy and mechanism Various CPUs today support multiple idle levels that are differentiated by varying exit latencies and power consumption during idle. Idle policy (governor) is differentiated from idle mechanism (driver). available_governors: (RO) displays a space separated list of available governors. current_driver: (RO) displays current idle mechanism. current_governor: (RW) displays current idle policy. Users can switch the governor at runtime by writing to this file. current_governor_ro: (RO) displays current idle policy. See Documentation/admin-guide/pm/cpuidle.rst and Documentation/driver-api/pm/cpuidle.rst for more information. What: /sys/devices/system/cpu/cpuX/cpuidle/state/name /sys/devices/system/cpu/cpuX/cpuidle/stateN/latency /sys/devices/system/cpu/cpuX/cpuidle/stateN/power /sys/devices/system/cpu/cpuX/cpuidle/stateN/time /sys/devices/system/cpu/cpuX/cpuidle/stateN/usage /sys/devices/system/cpu/cpuX/cpuidle/stateN/above /sys/devices/system/cpu/cpuX/cpuidle/stateN/below Date: September 2007 KernelVersion: v2.6.24 Contact: Linux power management list Description: The directory /sys/devices/system/cpu/cpuX/cpuidle contains per logical CPU specific cpuidle information for each online cpu X. The processor idle states which are available for use have the following attributes: ======== ==== ================================================= name: (RO) Name of the idle state (string). latency: (RO) The latency to exit out of this idle state (in microseconds). power: (RO) The power consumed while in this idle state (in milliwatts). time: (RO) The total time spent in this idle state (in microseconds). usage: (RO) Number of times this state was entered (a count). above: (RO) Number of times this state was entered, but the observed CPU idle duration was too short for it (a count). below: (RO) Number of times this state was entered, but the observed CPU idle duration was too long for it (a count). ======== ==== ================================================= What: /sys/devices/system/cpu/cpuX/cpuidle/state/desc Date: February 2008 KernelVersion: v2.6.25 Contact: Linux power management list Description: (RO) A small description about the idle state (string). What: /sys/devices/system/cpu/cpuX/cpuidle/state/disable Date: March 2012 KernelVersion: v3.10 Contact: Linux power management list Description: (RW) Option to disable this idle state (bool). The behavior and the effect of the disable variable depends on the implementation of a particular governor. In the ladder governor, for example, it is not coherent, i.e. if one is disabling a light state, then all deeper states are disabled as well, but the disable variable does not reflect it. Likewise, if one enables a deep state but a lighter state still is disabled, then this has no effect. What: /sys/devices/system/cpu/cpuX/cpuidle/state/default_status Date: December 2019 KernelVersion: v5.6 Contact: Linux power management list Description: (RO) The default status of this state, "enabled" or "disabled". What: /sys/devices/system/cpu/cpuX/cpuidle/state/residency Date: March 2014 KernelVersion: v3.15 Contact: Linux power management list Description: (RO) Display the target residency i.e. the minimum amount of time (in microseconds) this cpu should spend in this idle state to make the transition worth the effort. What: /sys/devices/system/cpu/cpuX/cpuidle/state/s2idle/ Date: March 2018 KernelVersion: v4.17 Contact: Linux power management list Description: Idle state usage statistics related to suspend-to-idle. This attribute group is only present for states that can be used in suspend-to-idle with suspended timekeeping. What: /sys/devices/system/cpu/cpuX/cpuidle/state/s2idle/time Date: March 2018 KernelVersion: v4.17 Contact: Linux power management list Description: Total time spent by the CPU in suspend-to-idle (with scheduler tick suspended) after requesting this state. What: /sys/devices/system/cpu/cpuX/cpuidle/state/s2idle/usage Date: March 2018 KernelVersion: v4.17 Contact: Linux power management list Description: Total number of times this state has been requested by the CPU while entering suspend-to-idle. What: /sys/devices/system/cpu/cpuX/cpufreq/* Date: pre-git history Contact: linux-pm@vger.kernel.org Description: Discover and change clock speed of CPUs Clock scaling allows you to change the clock speed of the CPUs on the fly. This is a nice method to save battery power, because the lower the clock speed, the less power the CPU consumes. There are many knobs to tweak in this directory. See files in Documentation/cpu-freq/ for more information. What: /sys/devices/system/cpu/cpuX/cpufreq/freqdomain_cpus Date: June 2013 Contact: linux-pm@vger.kernel.org Description: Discover CPUs in the same CPU frequency coordination domain freqdomain_cpus is the list of CPUs (online+offline) that share the same clock/freq domain (possibly at the hardware level). That information may be hidden from the cpufreq core and the value of related_cpus may be different from freqdomain_cpus. This attribute is useful for user space DVFS controllers to get better power/performance results for platforms using acpi-cpufreq. This file is only present if the acpi-cpufreq or the cppc-cpufreq drivers are in use. What: /sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1} Date: August 2008 KernelVersion: 2.6.27 Contact: Linux kernel mailing list Description: Disable L3 cache indices These files exist in every CPU's cache/index3 directory. Each cache_disable_{0,1} file corresponds to one disable slot which can be used to disable a cache index. Reading from these files on a processor with this functionality will return the currently disabled index for that node. There is one L3 structure per node, or per internal node on MCM machines. Writing a valid index to one of these files will cause the specified cache index to be disabled. All AMD processors with L3 caches provide this functionality. For details, see BKDGs at https://www.amd.com/en/support/tech-docs?keyword=bios+kernel What: /sys/devices/system/cpu/cpufreq/boost Date: August 2012 Contact: Linux kernel mailing list Description: Processor frequency boosting control This switch controls the boost setting for the whole system. Boosting allows the CPU and the firmware to run at a frequency beyond its nominal limit. More details can be found in Documentation/admin-guide/pm/cpufreq.rst What: /sys/devices/system/cpu/cpuX/crash_notes /sys/devices/system/cpu/cpuX/crash_notes_size Date: April 2013 Contact: kexec@lists.infradead.org Description: address and size of the percpu note. crash_notes: the physical address of the memory that holds the note of cpuX. crash_notes_size: size of the note of cpuX. What: /sys/devices/system/cpu/intel_pstate/max_perf_pct /sys/devices/system/cpu/intel_pstate/min_perf_pct /sys/devices/system/cpu/intel_pstate/no_turbo Date: February 2013 Contact: linux-pm@vger.kernel.org Description: Parameters for the Intel P-state driver Logic for selecting the current P-state in Intel Sandybridge+ processors. The three knobs control limits for the P-state that will be requested by the driver. max_perf_pct: limits the maximum P state that will be requested by the driver stated as a percentage of the available performance. min_perf_pct: limits the minimum P state that will be requested by the driver stated as a percentage of the available performance. no_turbo: limits the driver to selecting P states below the turbo frequency range. More details can be found in Documentation/admin-guide/pm/intel_pstate.rst What: /sys/devices/system/cpu/cpu*/cache/index*/ Date: July 2014(documented, existed before August 2008) Contact: Sudeep Holla Linux kernel mailing list Description: Parameters for the CPU cache attributes allocation_policy: - WriteAllocate: allocate a memory location to a cache line on a cache miss because of a write - ReadAllocate: allocate a memory location to a cache line on a cache miss because of a read - ReadWriteAllocate: both writeallocate and readallocate attributes: LEGACY used only on IA64 and is same as write_policy coherency_line_size: the minimum amount of data in bytes that gets transferred from memory to cache level: the cache hierarchy in the multi-level cache configuration number_of_sets: total number of sets in the cache, a set is a collection of cache lines with the same cache index physical_line_partition: number of physical cache line per cache tag shared_cpu_list: the list of logical cpus sharing the cache shared_cpu_map: logical cpu mask containing the list of cpus sharing the cache size: the total cache size in kB type: - Instruction: cache that only holds instructions - Data: cache that only caches data - Unified: cache that holds both data and instructions ways_of_associativity: degree of freedom in placing a particular block of memory in the cache write_policy: - WriteThrough: data is written to both the cache line and to the block in the lower-level memory - WriteBack: data is written only to the cache line and the modified cache line is written to main memory only when it is replaced What: /sys/devices/system/cpu/cpu*/cache/index*/id Date: September 2016 Contact: Linux kernel mailing list Description: Cache id The id provides a unique number for a specific instance of a cache of a particular type. E.g. there may be a level 3 unified cache on each socket in a server and we may assign them ids 0, 1, 2, ... Note that id value can be non-contiguous. E.g. level 1 caches typically exist per core, but there may not be a power of two cores on a socket, so these caches may be numbered 0, 1, 2, 3, 4, 5, 8, 9, 10, ... What: /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/turbo_stat /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/sub_turbo_stat /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/unthrottle /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/powercap /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overtemp /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/supply_fault /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overcurrent /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/occ_reset Date: March 2016 Contact: Linux kernel mailing list Linux for PowerPC mailing list Description: POWERNV CPUFreq driver's frequency throttle stats directory and attributes 'cpuX/cpufreq/throttle_stats' directory contains the CPU frequency throttle stat attributes for the chip. The throttle stats of a cpu is common across all the cpus belonging to a chip. Below are the throttle attributes exported in the 'throttle_stats' directory: - turbo_stat : This file gives the total number of times the max frequency is throttled to lower frequency in turbo (at and above nominal frequency) range of frequencies. - sub_turbo_stat : This file gives the total number of times the max frequency is throttled to lower frequency in sub-turbo(below nominal frequency) range of frequencies. - unthrottle : This file gives the total number of times the max frequency is unthrottled after being throttled. - powercap : This file gives the total number of times the max frequency is throttled due to 'Power Capping'. - overtemp : This file gives the total number of times the max frequency is throttled due to 'CPU Over Temperature'. - supply_fault : This file gives the total number of times the max frequency is throttled due to 'Power Supply Failure'. - overcurrent : This file gives the total number of times the max frequency is throttled due to 'Overcurrent'. - occ_reset : This file gives the total number of times the max frequency is throttled due to 'OCC Reset'. The sysfs attributes representing different throttle reasons like powercap, overtemp, supply_fault, overcurrent and occ_reset map to the reasons provided by OCC firmware for throttling the frequency. What: /sys/devices/system/cpu/cpufreq/policyX/throttle_stats /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/turbo_stat /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/sub_turbo_stat /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/unthrottle /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/powercap /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overtemp /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/supply_fault /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overcurrent /sys/devices/system/cpu/cpufreq/policyX/throttle_stats/occ_reset Date: March 2016 Contact: Linux kernel mailing list Linux for PowerPC mailing list Description: POWERNV CPUFreq driver's frequency throttle stats directory and attributes 'policyX/throttle_stats' directory and all the attributes are same as the /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats directory and attributes which give the frequency throttle information of the chip. What: /sys/devices/system/cpu/cpuX/regs/ /sys/devices/system/cpu/cpuX/regs/identification/ /sys/devices/system/cpu/cpuX/regs/identification/midr_el1 /sys/devices/system/cpu/cpuX/regs/identification/revidr_el1 /sys/devices/system/cpu/cpuX/regs/identification/smidr_el1 Date: June 2016 Contact: Linux ARM Kernel Mailing list Description: AArch64 CPU registers 'identification' directory exposes the CPU ID registers for identifying model and revision of the CPU and SMCU. What: /sys/devices/system/cpu/aarch32_el0 Date: May 2021 Contact: Linux ARM Kernel Mailing list Description: Identifies the subset of CPUs in the system that can execute AArch32 (32-bit ARM) applications. If present, the same format as /sys/devices/system/cpu/{offline,online,possible,present} is used. If absent, then all or none of the CPUs can execute AArch32 applications and execve() will behave accordingly. What: /sys/devices/system/cpu/cpuX/cpu_capacity Date: December 2016 Contact: Linux kernel mailing list Description: information about CPUs heterogeneity. cpu_capacity: capacity of cpuX. What: /sys/devices/system/cpu/vulnerabilities /sys/devices/system/cpu/vulnerabilities/gather_data_sampling /sys/devices/system/cpu/vulnerabilities/itlb_multihit /sys/devices/system/cpu/vulnerabilities/l1tf /sys/devices/system/cpu/vulnerabilities/mds /sys/devices/system/cpu/vulnerabilities/meltdown /sys/devices/system/cpu/vulnerabilities/mmio_stale_data /sys/devices/system/cpu/vulnerabilities/reg_file_data_sampling /sys/devices/system/cpu/vulnerabilities/retbleed /sys/devices/system/cpu/vulnerabilities/spec_store_bypass /sys/devices/system/cpu/vulnerabilities/spectre_v1 /sys/devices/system/cpu/vulnerabilities/spectre_v2 /sys/devices/system/cpu/vulnerabilities/srbds /sys/devices/system/cpu/vulnerabilities/tsx_async_abort Date: January 2018 Contact: Linux kernel mailing list Description: Information about CPU vulnerabilities The files are named after the code names of CPU vulnerabilities. The output of those files reflects the state of the CPUs in the system. Possible output values: ================ ============================================== "Not affected" CPU is not affected by the vulnerability "Vulnerable" CPU is affected and no mitigation in effect "Mitigation: $M" CPU is affected and mitigation $M is in effect ================ ============================================== See also: Documentation/admin-guide/hw-vuln/index.rst What: /sys/devices/system/cpu/smt /sys/devices/system/cpu/smt/active /sys/devices/system/cpu/smt/control Date: June 2018 Contact: Linux kernel mailing list Description: Control Symmetric Multi Threading (SMT) active: Tells whether SMT is active (enabled and siblings online) control: Read/write interface to control SMT. Possible values: ================ ========================================= "on" SMT is enabled "off" SMT is disabled "" SMT is enabled with N threads per core. "forceoff" SMT is force disabled. Cannot be changed. "notsupported" SMT is not supported by the CPU "notimplemented" SMT runtime toggling is not implemented for the architecture ================ ========================================= If control status is "forceoff" or "notsupported" writes are rejected. What: /sys/devices/system/cpu/cpuX/power/energy_perf_bias Date: March 2019 Contact: linux-pm@vger.kernel.org Description: Intel Energy and Performance Bias Hint (EPB) EPB for the given CPU in a sliding scale 0 - 15, where a value of 0 corresponds to a hint preference for highest performance and a value of 15 corresponds to the maximum energy savings. In order to change the EPB value for the CPU, write either a number in the 0 - 15 sliding scale above, or one of the strings: "performance", "balance-performance", "normal", "balance-power", "power" (that represent values reflected by their meaning), to this attribute. This attribute is present for all online CPUs supporting the Intel EPB feature. What: /sys/devices/system/cpu/umwait_control /sys/devices/system/cpu/umwait_control/enable_c02 /sys/devices/system/cpu/umwait_control/max_time Date: May 2019 Contact: Linux kernel mailing list Description: Umwait control enable_c02: Read/write interface to control umwait C0.2 state Read returns C0.2 state status: 0: C0.2 is disabled 1: C0.2 is enabled Write 'y' or '1' or 'on' to enable C0.2 state. Write 'n' or '0' or 'off' to disable C0.2 state. The interface is case insensitive. max_time: Read/write interface to control umwait maximum time in TSC-quanta that the CPU can reside in either C0.1 or C0.2 state. The time is an unsigned 32-bit number. Note that a value of zero means there is no limit. Low order two bits must be zero. What: /sys/devices/system/cpu/svm Date: August 2019 Contact: Linux kernel mailing list Linux for PowerPC mailing list Description: Secure Virtual Machine If 1, it means the system is using the Protected Execution Facility in POWER9 and newer processors. i.e., it is a Secure Virtual Machine. What: /sys/devices/system/cpu/cpuX/purr Date: Apr 2005 Contact: Linux for PowerPC mailing list Description: PURR ticks for this CPU since the system boot. The Processor Utilization Resources Register (PURR) is a 64-bit counter which provides an estimate of the resources used by the CPU thread. The contents of this register increases monotonically. This sysfs interface exposes the number of PURR ticks for cpuX. What: /sys/devices/system/cpu/cpuX/spurr Date: Dec 2006 Contact: Linux for PowerPC mailing list Description: SPURR ticks for this CPU since the system boot. The Scaled Processor Utilization Resources Register (SPURR) is a 64-bit counter that provides a frequency invariant estimate of the resources used by the CPU thread. The contents of this register increases monotonically. This sysfs interface exposes the number of SPURR ticks for cpuX. What: /sys/devices/system/cpu/cpuX/idle_purr Date: Apr 2020 Contact: Linux for PowerPC mailing list Description: PURR ticks for cpuX when it was idle. This sysfs interface exposes the number of PURR ticks for cpuX when it was idle. What: /sys/devices/system/cpu/cpuX/idle_spurr Date: Apr 2020 Contact: Linux for PowerPC mailing list Description: SPURR ticks for cpuX when it was idle. This sysfs interface exposes the number of SPURR ticks for cpuX when it was idle. What: /sys/devices/system/cpu/cpuX/mte_tcf_preferred Date: July 2021 Contact: Linux ARM Kernel Mailing list Description: Preferred MTE tag checking mode When a user program specifies more than one MTE tag checking mode, this sysfs node is used to specify which mode should be preferred when scheduling a task on that CPU. Possible values: ================ ============================================== "sync" Prefer synchronous mode "asymm" Prefer asymmetric mode "async" Prefer asynchronous mode ================ ============================================== See also: Documentation/arch/arm64/memory-tagging-extension.rst What: /sys/devices/system/cpu/nohz_full Date: Apr 2015 Contact: Linux kernel mailing list Description: (RO) the list of CPUs that are in nohz_full mode. These CPUs are set by boot parameter "nohz_full=". What: /sys/devices/system/cpu/isolated Date: Apr 2015 Contact: Linux kernel mailing list Description: (RO) the list of CPUs that are isolated and don't participate in load balancing. These CPUs are set by boot parameter "isolcpus=". What: /sys/devices/system/cpu/crash_hotplug Date: Aug 2023 Contact: Linux kernel mailing list Description: (RO) indicates whether or not the kernel directly supports modifying the crash elfcorehdr for CPU hot un/plug and/or on/offline changes.