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/cputopology.txt 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/cputopology.txt for more information.
 107
 108
 109 What:           /sys/devices/system/cpu/cpuidle/current_driver
 110                 /sys/devices/system/cpu/cpuidle/current_governer_ro
 111 Date:           September 2007
 112 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 113 Description:    Discover cpuidle policy and mechanism
 114
 115                 Various CPUs today support multiple idle levels that are
 116                 differentiated by varying exit latencies and power
 117                 consumption during idle.
 118
 119                 Idle policy (governor) is differentiated from idle mechanism
 120                 (driver)
 121
 122                 current_driver: displays current idle mechanism
 123
 124                 current_governor_ro: displays current idle policy
 125
 126                 See files in Documentation/cpuidle/ for more information.
 127
 128
 129 What:           /sys/devices/system/cpu/cpu#/cpufreq/*
 130 Date:           pre-git history
 131 Contact:        linux-pm@vger.kernel.org
 132 Description:    Discover and change clock speed of CPUs
 133
 134                 Clock scaling allows you to change the clock speed of the
 135                 CPUs on the fly. This is a nice method to save battery
 136                 power, because the lower the clock speed, the less power
 137                 the CPU consumes.
 138
 139                 There are many knobs to tweak in this directory.
 140
 141                 See files in Documentation/cpu-freq/ for more information.
 142
 143                 In particular, read Documentation/cpu-freq/user-guide.txt
 144                 to learn how to control the knobs.
 145
 146
 147 What:           /sys/devices/system/cpu/cpu#/cpufreq/freqdomain_cpus
 148 Date:           June 2013
 149 Contact:        linux-pm@vger.kernel.org
 150 Description:    Discover CPUs in the same CPU frequency coordination domain
 151
 152                 freqdomain_cpus is the list of CPUs (online+offline) that share
 153                 the same clock/freq domain (possibly at the hardware level).
 154                 That information may be hidden from the cpufreq core and the
 155                 value of related_cpus may be different from freqdomain_cpus. This
 156                 attribute is useful for user space DVFS controllers to get better
 157                 power/performance results for platforms using acpi-cpufreq.
 158
 159                 This file is only present if the acpi-cpufreq driver is in use.
 160
 161
 162 What:           /sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
 163 Date:           August 2008
 164 KernelVersion:  2.6.27
 165 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 166 Description:    Disable L3 cache indices
 167
 168                 These files exist in every CPU's cache/index3 directory. Each
 169                 cache_disable_{0,1} file corresponds to one disable slot which
 170                 can be used to disable a cache index. Reading from these files
 171                 on a processor with this functionality will return the currently
 172                 disabled index for that node. There is one L3 structure per
 173                 node, or per internal node on MCM machines. Writing a valid
 174                 index to one of these files will cause the specificed cache
 175                 index to be disabled.
 176
 177                 All AMD processors with L3 caches provide this functionality.
 178                 For details, see BKDGs at
 179                 http://developer.amd.com/documentation/guides/Pages/default.aspx
 180
 181
 182 What:           /sys/devices/system/cpu/cpufreq/boost
 183 Date:           August 2012
 184 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 185 Description:    Processor frequency boosting control
 186
 187                 This switch controls the boost setting for the whole system.
 188                 Boosting allows the CPU and the firmware to run at a frequency
 189                 beyound it's nominal limit.
 190                 More details can be found in Documentation/cpu-freq/boost.txt
 191
 192
 193 What:           /sys/devices/system/cpu/cpu#/crash_notes
 194                 /sys/devices/system/cpu/cpu#/crash_notes_size
 195 Date:           April 2013
 196 Contact:        kexec@lists.infradead.org
 197 Description:    address and size of the percpu note.
 198
 199                 crash_notes: the physical address of the memory that holds the
 200                 note of cpu#.
 201
 202                 crash_notes_size: size of the note of cpu#.
 203
 204
 205 What:           /sys/devices/system/cpu/intel_pstate/max_perf_pct
 206                 /sys/devices/system/cpu/intel_pstate/min_perf_pct
 207                 /sys/devices/system/cpu/intel_pstate/no_turbo
 208 Date:           February 2013
 209 Contact:        linux-pm@vger.kernel.org
 210 Description:    Parameters for the Intel P-state driver
 211
 212                 Logic for selecting the current P-state in Intel
 213                 Sandybridge+ processors. The three knobs control
 214                 limits for the P-state that will be requested by the
 215                 driver.
 216
 217                 max_perf_pct: limits the maximum P state that will be requested by
 218                 the driver stated as a percentage of the available performance.
 219
 220                 min_perf_pct: limits the minimum P state that will be requested by
 221                 the driver stated as a percentage of the available performance.
 222
 223                 no_turbo: limits the driver to selecting P states below the turbo
 224                 frequency range.
 225
 226                 More details can be found in Documentation/cpu-freq/intel-pstate.txt
 227
 228 What:           /sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below>
 229 Date:           July 2014(documented, existed before August 2008)
 230 Contact:        Sudeep Holla <sudeep.holla@arm.com>
 231                 Linux kernel mailing list <linux-kernel@vger.kernel.org>
 232 Description:    Parameters for the CPU cache attributes
 233
 234                 allocation_policy:
 235                         - WriteAllocate: allocate a memory location to a cache line
 236                                          on a cache miss because of a write
 237                         - ReadAllocate: allocate a memory location to a cache line
 238                                         on a cache miss because of a read
 239                         - ReadWriteAllocate: both writeallocate and readallocate
 240
 241                 attributes: LEGACY used only on IA64 and is same as write_policy
 242
 243                 coherency_line_size: the minimum amount of data in bytes that gets
 244                                      transferred from memory to cache
 245
 246                 level: the cache hierarchy in the multi-level cache configuration
 247
 248                 number_of_sets: total number of sets in the cache, a set is a
 249                                 collection of cache lines with the same cache index
 250
 251                 physical_line_partition: number of physical cache line per cache tag
 252
 253                 shared_cpu_list: the list of logical cpus sharing the cache
 254
 255                 shared_cpu_map: logical cpu mask containing the list of cpus sharing
 256                                 the cache
 257
 258                 size: the total cache size in kB
 259
 260                 type:
 261                         - Instruction: cache that only holds instructions
 262                         - Data: cache that only caches data
 263                         - Unified: cache that holds both data and instructions
 264
 265                 ways_of_associativity: degree of freedom in placing a particular block
 266                                         of memory in the cache
 267
 268                 write_policy:
 269                         - WriteThrough: data is written to both the cache line
 270                                         and to the block in the lower-level memory
 271                         - WriteBack: data is written only to the cache line and
 272                                      the modified cache line is written to main
 273                                      memory only when it is replaced