Documentation/cpu-freq/cpufreq-stats.txt

   1
   2      CPU frequency and voltage scaling statistics in the Linux(TM) kernel
   3
   4
   5              L i n u x    c p u f r e q - s t a t s   d r i v e r
   6
   7                        - information for users -
   8
   9
  10              Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
  11
  12 Contents
  13 1. Introduction
  14 2. Statistics Provided (with example)
  15 3. Configuring cpufreq-stats
  16
  17
  18 1. Introduction
  19
  20 cpufreq-stats is a driver that provides CPU frequency statistics for each CPU.
  21 These statistics are provided in /sysfs as a bunch of read_only interfaces. This
  22 interface (when configured) will appear in a separate directory under cpufreq
  23 in /sysfs (<sysfs root>/devices/system/cpu/cpuX/cpufreq/stats/) for each CPU.
  24 Various statistics will form read_only files under this directory.
  25
  26 This driver is designed to be independent of any particular cpufreq_driver
  27 that may be running on your CPU. So, it will work with any cpufreq_driver.
  28
  29
  30 2. Statistics Provided (with example)
  31
  32 cpufreq stats provides following statistics (explained in detail below).
  33 -  time_in_state
  34 -  total_trans
  35 -  trans_table
  36
  37 All the statistics will be from the time the stats driver has been inserted
  38 (or the time the stats were reset) to the time when a read of a particular
  39 statistic is done. Obviously, stats driver will not have any information
  40 about the frequency transitions before the stats driver insertion.
  41
  42 --------------------------------------------------------------------------------
  43 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l
  44 total 0
  45 drwxr-xr-x  2 root root    0 May 14 16:06 .
  46 drwxr-xr-x  3 root root    0 May 14 15:58 ..
  47 --w-------  1 root root 4096 May 14 16:06 reset
  48 -r--r--r--  1 root root 4096 May 14 16:06 time_in_state
  49 -r--r--r--  1 root root 4096 May 14 16:06 total_trans
  50 -r--r--r--  1 root root 4096 May 14 16:06 trans_table
  51 --------------------------------------------------------------------------------
  52
  53 -  reset
  54 Write-only attribute that can be used to reset the stat counters. This can be
  55 useful for evaluating system behaviour under different governors without the
  56 need for a reboot.
  57
  58 -  time_in_state
  59 This gives the amount of time spent in each of the frequencies supported by
  60 this CPU. The cat output will have "<frequency> <time>" pair in each line, which
  61 will mean this CPU spent <time> usertime units of time at <frequency>. Output
  62 will have one line for each of the supported frequencies. usertime units here
  63 is 10mS (similar to other time exported in /proc).
  64
  65 --------------------------------------------------------------------------------
  66 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state
  67 3600000 2089
  68 3400000 136
  69 3200000 34
  70 3000000 67
  71 2800000 172488
  72 --------------------------------------------------------------------------------
  73
  74
  75 -  total_trans
  76 This gives the total number of frequency transitions on this CPU. The cat
  77 output will have a single count which is the total number of frequency
  78 transitions.
  79
  80 --------------------------------------------------------------------------------
  81 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans
  82 20
  83 --------------------------------------------------------------------------------
  84
  85 -  trans_table
  86 This will give a fine grained information about all the CPU frequency
  87 transitions. The cat output here is a two dimensional matrix, where an entry
  88 <i,j> (row i, column j) represents the count of number of transitions from
  89 Freq_i to Freq_j. Freq_i is in descending order with increasing rows and
  90 Freq_j is in descending order with increasing columns. The output here also
  91 contains the actual freq values for each row and column for better readability.
  92
  93 --------------------------------------------------------------------------------
  94 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table
  95    From  :    To
  96          :   3600000   3400000   3200000   3000000   2800000
  97   3600000:         0         5         0         0         0
  98   3400000:         4         0         2         0         0
  99   3200000:         0         1         0         2         0
 100   3000000:         0         0         1         0         3
 101   2800000:         0         0         0         2         0
 102 --------------------------------------------------------------------------------
 103
 104
 105 3. Configuring cpufreq-stats
 106
 107 To configure cpufreq-stats in your kernel
 108 Config Main Menu
 109         Power management options (ACPI, APM)  --->
 110                 CPU Frequency scaling  --->
 111                         [*] CPU Frequency scaling
 112                         [*]   CPU frequency translation statistics
 113
 114
 115 "CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure
 116 cpufreq-stats.
 117
 118 "CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the
 119 statistics which includes time_in_state, total_trans and trans_table.
 120
 121 Once this option is enabled and your CPU supports cpufrequency, you
 122 will be able to see the CPU frequency statistics in /sysfs.