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/sched_mc_power_savings
  13                 /sys/devices/system/cpu/sched_smt_power_savings
  14 Date:           June 2006
  15 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
  16 Description:    Discover and adjust the kernel's multi-core scheduler support.
  17
  18                 Possible values are:
  19
  20                 0 - No power saving load balance (default value)
  21                 1 - Fill one thread/core/package first for long running threads
  22                 2 - Also bias task wakeups to semi-idle cpu package for power
  23                     savings
  24
  25                 sched_mc_power_savings is dependent upon SCHED_MC, which is
  26                 itself architecture dependent.
  27
  28                 sched_smt_power_savings is dependent upon SCHED_SMT, which
  29                 is itself architecture dependent.
  30
  31                 The two files are independent of each other. It is possible
  32                 that one file may be present without the other.
  33
  34                 Introduced by git commit 5c45bf27.
  35
  36
  37 What:           /sys/devices/system/cpu/kernel_max
  38                 /sys/devices/system/cpu/offline
  39                 /sys/devices/system/cpu/online
  40                 /sys/devices/system/cpu/possible
  41                 /sys/devices/system/cpu/present
  42 Date:           December 2008
  43 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
  44 Description:    CPU topology files that describe kernel limits related to
  45                 hotplug. Briefly:
  46
  47                 kernel_max: the maximum cpu index allowed by the kernel
  48                 configuration.
  49
  50                 offline: cpus that are not online because they have been
  51                 HOTPLUGGED off or exceed the limit of cpus allowed by the
  52                 kernel configuration (kernel_max above).
  53
  54                 online: cpus that are online and being scheduled.
  55
  56                 possible: cpus that have been allocated resources and can be
  57                 brought online if they are present.
  58
  59                 present: cpus that have been identified as being present in
  60                 the system.
  61
  62                 See Documentation/cputopology.txt for more information.
  63
  64
  65 What:           /sys/devices/system/cpu/probe
  66                 /sys/devices/system/cpu/release
  67 Date:           November 2009
  68 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
  69 Description:    Dynamic addition and removal of CPU's.  This is not hotplug
  70                 removal, this is meant complete removal/addition of the CPU
  71                 from the system.
  72
  73                 probe: writes to this file will dynamically add a CPU to the
  74                 system.  Information written to the file to add CPU's is
  75                 architecture specific.
  76
  77                 release: writes to this file dynamically remove a CPU from
  78                 the system.  Information writtento the file to remove CPU's
  79                 is architecture specific.
  80
  81 What:           /sys/devices/system/cpu/cpu#/node
  82 Date:           October 2009
  83 Contact:        Linux memory management mailing list <linux-mm@kvack.org>
  84 Description:    Discover NUMA node a CPU belongs to
  85
  86                 When CONFIG_NUMA is enabled, a symbolic link that points
  87                 to the corresponding NUMA node directory.
  88
  89                 For example, the following symlink is created for cpu42
  90                 in NUMA node 2:
  91
  92                 /sys/devices/system/cpu/cpu42/node2 -> ../../node/node2
  93
  94
  95 What:           /sys/devices/system/cpu/cpu#/topology/core_id
  96                 /sys/devices/system/cpu/cpu#/topology/core_siblings
  97                 /sys/devices/system/cpu/cpu#/topology/core_siblings_list
  98                 /sys/devices/system/cpu/cpu#/topology/physical_package_id
  99                 /sys/devices/system/cpu/cpu#/topology/thread_siblings
 100                 /sys/devices/system/cpu/cpu#/topology/thread_siblings_list
 101 Date:           December 2008
 102 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 103 Description:    CPU topology files that describe a logical CPU's relationship
 104                 to other cores and threads in the same physical package.
 105
 106                 One cpu# directory is created per logical CPU in the system,
 107                 e.g. /sys/devices/system/cpu/cpu42/.
 108
 109                 Briefly, the files above are:
 110
 111                 core_id: the CPU core ID of cpu#. Typically it is the
 112                 hardware platform's identifier (rather than the kernel's).
 113                 The actual value is architecture and platform dependent.
 114
 115                 core_siblings: internal kernel map of cpu#'s hardware threads
 116                 within the same physical_package_id.
 117
 118                 core_siblings_list: human-readable list of the logical CPU
 119                 numbers within the same physical_package_id as cpu#.
 120
 121                 physical_package_id: physical package id of cpu#. Typically
 122                 corresponds to a physical socket number, but the actual value
 123                 is architecture and platform dependent.
 124
 125                 thread_siblings: internel kernel map of cpu#'s hardware
 126                 threads within the same core as cpu#
 127
 128                 thread_siblings_list: human-readable list of cpu#'s hardware
 129                 threads within the same core as cpu#
 130
 131                 See Documentation/cputopology.txt for more information.
 132
 133
 134 What:           /sys/devices/system/cpu/cpuidle/current_driver
 135                 /sys/devices/system/cpu/cpuidle/current_governer_ro
 136 Date:           September 2007
 137 Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>
 138 Description:    Discover cpuidle policy and mechanism
 139
 140                 Various CPUs today support multiple idle levels that are
 141                 differentiated by varying exit latencies and power
 142                 consumption during idle.
 143
 144                 Idle policy (governor) is differentiated from idle mechanism
 145                 (driver)
 146
 147                 current_driver: displays current idle mechanism
 148
 149                 current_governor_ro: displays current idle policy
 150
 151                 See files in Documentation/cpuidle/ for more information.
 152
 153
 154 What:           /sys/devices/system/cpu/cpu#/cpufreq/*
 155 Date:           pre-git history
 156 Contact:        cpufreq@vger.kernel.org
 157 Description:    Discover and change clock speed of CPUs
 158
 159                 Clock scaling allows you to change the clock speed of the
 160                 CPUs on the fly. This is a nice method to save battery
 161                 power, because the lower the clock speed, the less power
 162                 the CPU consumes.
 163
 164                 There are many knobs to tweak in this directory.
 165
 166                 See files in Documentation/cpu-freq/ for more information.
 167
 168                 In particular, read Documentation/cpu-freq/user-guide.txt
 169                 to learn how to control the knobs.
 170
 171
 172 What:      /sys/devices/system/cpu/cpu*/cache/index*/cache_disable_X
 173 Date:      August 2008
 174 KernelVersion:  2.6.27
 175 Contact:        mark.langsdorf@amd.com
 176 Description:    These files exist in every cpu's cache index directories.
 177                 There are currently 2 cache_disable_# files in each
 178                 directory.  Reading from these files on a supported
 179                 processor will return that cache disable index value
 180                 for that processor and node.  Writing to one of these
 181                 files will cause the specificed cache index to be disabled.
 182
 183                 Currently, only AMD Family 10h Processors support cache index
 184                 disable, and only for their L3 caches.  See the BIOS and
 185                 Kernel Developer's Guide at
 186                 http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/31116-Public-GH-BKDG_3.20_2-4-09.pdf
 187                 for formatting information and other details on the
 188                 cache index disable.
 189 Users:    joachim.deguara@amd.com