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 to the time when a read of a particular statistic is done. Obviously, stats
  39 driver will not have any information about the frequency transitions before
  40 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 -r--r--r--  1 root root 4096 May 14 16:06 time_in_state
  48 -r--r--r--  1 root root 4096 May 14 16:06 total_trans
  49 -r--r--r--  1 root root 4096 May 14 16:06 trans_table
  50 --------------------------------------------------------------------------------
  51
  52 -  time_in_state
  53 This gives the amount of time spent in each of the frequencies supported by
  54 this CPU. The cat output will have "<frequency> <time>" pair in each line, which
  55 will mean this CPU spent <time> usertime units of time at <frequency>. Output
  56 will have one line for each of the supported frequencies. usertime units here
  57 is 10mS (similar to other time exported in /proc).
  58
  59 --------------------------------------------------------------------------------
  60 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state
  61 3600000 2089
  62 3400000 136
  63 3200000 34
  64 3000000 67
  65 2800000 172488
  66 --------------------------------------------------------------------------------
  67
  68
  69 -  total_trans
  70 This gives the total number of frequency transitions on this CPU. The cat
  71 output will have a single count which is the total number of frequency
  72 transitions.
  73
  74 --------------------------------------------------------------------------------
  75 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans
  76 20
  77 --------------------------------------------------------------------------------
  78
  79 -  trans_table
  80 This will give a fine grained information about all the CPU frequency
  81 transitions. The cat output here is a two dimensional matrix, where an entry
  82 <i,j> (row i, column j) represents the count of number of transitions from
  83 Freq_i to Freq_j. Freq_i is in descending order with increasing rows and
  84 Freq_j is in descending order with increasing columns. The output here also
  85 contains the actual freq values for each row and column for better readability.
  86
  87 --------------------------------------------------------------------------------
  88 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table
  89    From  :    To
  90          :   3600000   3400000   3200000   3000000   2800000
  91   3600000:         0         5         0         0         0
  92   3400000:         4         0         2         0         0
  93   3200000:         0         1         0         2         0
  94   3000000:         0         0         1         0         3
  95   2800000:         0         0         0         2         0
  96 --------------------------------------------------------------------------------
  97
  98
  99 3. Configuring cpufreq-stats
 100
 101 To configure cpufreq-stats in your kernel
 102 Config Main Menu
 103         Power management options (ACPI, APM)  --->
 104                 CPU Frequency scaling  --->
 105                         [*] CPU Frequency scaling
 106                         <*>   CPU frequency translation statistics
 107                         [*]     CPU frequency translation statistics details
 108
 109
 110 "CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure
 111 cpufreq-stats.
 112
 113 "CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the
 114 basic statistics which includes time_in_state and total_trans.
 115
 116 "CPU frequency translation statistics details" (CONFIG_CPU_FREQ_STAT_DETAILS)
 117 provides fine grained cpufreq stats by trans_table. The reason for having a
 118 separate config option for trans_table is:
 119 - trans_table goes against the traditional /sysfs rule of one value per
 120   interface. It provides a whole bunch of value in a 2 dimensional matrix
 121   form.
 122
 123 Once these two options are enabled and your CPU supports cpufrequency, you
 124 will be able to see the CPU frequency statistics in /sysfs.
 125
 126
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 128