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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
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  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
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 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.
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