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  2     CPU frequency and voltage scaling statistics in the Linux(TM) kernel
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  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
 38(or the time the stats were reset) to the time when a read of a particular
 39statistic is done. Obviously, stats driver will not have any information
 40about the frequency transitions before the 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--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
 54Write-only attribute that can be used to reset the stat counters. This can be
 55useful for evaluating system behaviour under different governors without the
 56need for a reboot.
 57
 58-  time_in_state
 59This gives the amount of time spent in each of the frequencies supported by
 60this CPU. The cat output will have "<frequency> <time>" pair in each line, which
 61will mean this CPU spent <time> usertime units of time at <frequency>. Output
 62will have one line for each of the supported frequencies. usertime units here 
 63is 10mS (similar to other time exported in /proc).
 64
 65--------------------------------------------------------------------------------
 66<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state 
 673600000 2089
 683400000 136
 693200000 34
 703000000 67
 712800000 172488
 72--------------------------------------------------------------------------------
 73
 74
 75-  total_trans
 76This gives the total number of frequency transitions on this CPU. The cat 
 77output will have a single count which is the total number of frequency
 78transitions.
 79
 80--------------------------------------------------------------------------------
 81<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans
 8220
 83--------------------------------------------------------------------------------
 84
 85-  trans_table
 86This will give a fine grained information about all the CPU frequency
 87transitions. 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 
 89Freq_i to Freq_j. Freq_i is in descending order with increasing rows and 
 90Freq_j is in descending order with increasing columns. The output here also 
 91contains the actual freq values for each row and column for better readability.
 92
 93If the transition table is bigger than PAGE_SIZE, reading this will
 94return an -EFBIG error.
 95
 96--------------------------------------------------------------------------------
 97<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table
 98   From  :    To
 99         :   3600000   3400000   3200000   3000000   2800000 
100  3600000:         0         5         0         0         0 
101  3400000:         4         0         2         0         0 
102  3200000:         0         1         0         2         0 
103  3000000:         0         0         1         0         3 
104  2800000:         0         0         0         2         0 
105--------------------------------------------------------------------------------
106
107
1083. Configuring cpufreq-stats
109
110To configure cpufreq-stats in your kernel
111Config Main Menu
112	Power management options (ACPI, APM)  --->
113		CPU Frequency scaling  --->
114			[*] CPU Frequency scaling
115			[*]   CPU frequency translation statistics
116
117
118"CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure
119cpufreq-stats.
120
121"CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the
122statistics which includes time_in_state, total_trans and trans_table.
123
124Once this option is enabled and your CPU supports cpufrequency, you
125will be able to see the CPU frequency statistics in /sysfs.