linux/Documentation/cpu-freq/cpufreq-stats.txt
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   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
  12Contents
  131. Introduction
  142. Statistics Provided (with example)
  153. Configuring cpufreq-stats
  16
  17
  181. Introduction
  19
  20cpufreq-stats is a driver that provides CPU frequency statistics for each CPU.
  21These statistics are provided in /sysfs as a bunch of read_only interfaces. This
  22interface (when configured) will appear in a separate directory under cpufreq
  23in /sysfs (<sysfs root>/devices/system/cpu/cpuX/cpufreq/stats/) for each CPU.
  24Various statistics will form read_only files under this directory.
  25
  26This driver is designed to be independent of any particular cpufreq_driver
  27that may be running on your CPU. So, it will work with any cpufreq_driver.
  28
  29
  302. Statistics Provided (with example)
  31
  32cpufreq stats provides following statistics (explained in detail below).
  33-  time_in_state
  34-  total_trans
  35-  trans_table
  36
  37All the statistics will be from the time the stats driver has been inserted 
  38to the time when a read of a particular statistic is done. Obviously, stats 
  39driver will not have any information about the frequency transitions before
  40the stats driver insertion.
  41
  42--------------------------------------------------------------------------------
  43<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l
  44total 0
  45drwxr-xr-x  2 root root    0 May 14 16:06 .
  46drwxr-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
  53This gives the amount of time spent in each of the frequencies supported by
  54this CPU. The cat output will have "<frequency> <time>" pair in each line, which
  55will mean this CPU spent <time> usertime units of time at <frequency>. Output
  56will have one line for each of the supported frequencies. usertime units here 
  57is 10mS (similar to other time exported in /proc).
  58
  59--------------------------------------------------------------------------------
  60<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state 
  613600000 2089
  623400000 136
  633200000 34
  643000000 67
  652800000 172488
  66--------------------------------------------------------------------------------
  67
  68
  69-  total_trans
  70This gives the total number of frequency transitions on this CPU. The cat 
  71output will have a single count which is the total number of frequency
  72transitions.
  73
  74--------------------------------------------------------------------------------
  75<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans
  7620
  77--------------------------------------------------------------------------------
  78
  79-  trans_table
  80This will give a fine grained information about all the CPU frequency
  81transitions. 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 
  83Freq_i to Freq_j. Freq_i is in descending order with increasing rows and 
  84Freq_j is in descending order with increasing columns. The output here also 
  85contains 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
  993. Configuring cpufreq-stats
 100
 101To configure cpufreq-stats in your kernel
 102Config 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
 111cpufreq-stats.
 112
 113"CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the
 114basic statistics which includes time_in_state and total_trans.
 115
 116"CPU frequency translation statistics details" (CONFIG_CPU_FREQ_STAT_DETAILS)
 117provides fine grained cpufreq stats by trans_table. The reason for having a
 118separate 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
 123Once these two options are enabled and your CPU supports cpufrequency, you
 124will be able to see the CPU frequency statistics in /sysfs.
 125
 126
 127
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 129
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