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Diffstat (limited to 'Documentation/cpu-freq/cpufreq-stats.txt')
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diff --git a/Documentation/cpu-freq/cpufreq-stats.txt b/Documentation/cpu-freq/cpufreq-stats.txt new file mode 100644 index 000000000..a873855c8 --- /dev/null +++ b/Documentation/cpu-freq/cpufreq-stats.txt @@ -0,0 +1,125 @@ + + CPU frequency and voltage scaling statistics in the Linux(TM) kernel + + + L i n u x c p u f r e q - s t a t s d r i v e r + + - information for users - + + + Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> + +Contents +1. Introduction +2. Statistics Provided (with example) +3. Configuring cpufreq-stats + + +1. Introduction + +cpufreq-stats is a driver that provides CPU frequency statistics for each CPU. +These statistics are provided in /sysfs as a bunch of read_only interfaces. This +interface (when configured) will appear in a separate directory under cpufreq +in /sysfs (<sysfs root>/devices/system/cpu/cpuX/cpufreq/stats/) for each CPU. +Various statistics will form read_only files under this directory. + +This driver is designed to be independent of any particular cpufreq_driver +that may be running on your CPU. So, it will work with any cpufreq_driver. + + +2. Statistics Provided (with example) + +cpufreq stats provides following statistics (explained in detail below). +- time_in_state +- total_trans +- trans_table + +All the statistics will be from the time the stats driver has been inserted +(or the time the stats were reset) to the time when a read of a particular +statistic is done. Obviously, stats driver will not have any information +about the frequency transitions before the stats driver insertion. + +-------------------------------------------------------------------------------- +<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l +total 0 +drwxr-xr-x 2 root root 0 May 14 16:06 . +drwxr-xr-x 3 root root 0 May 14 15:58 .. +--w------- 1 root root 4096 May 14 16:06 reset +-r--r--r-- 1 root root 4096 May 14 16:06 time_in_state +-r--r--r-- 1 root root 4096 May 14 16:06 total_trans +-r--r--r-- 1 root root 4096 May 14 16:06 trans_table +-------------------------------------------------------------------------------- + +- reset +Write-only attribute that can be used to reset the stat counters. This can be +useful for evaluating system behaviour under different governors without the +need for a reboot. + +- time_in_state +This gives the amount of time spent in each of the frequencies supported by +this CPU. The cat output will have "<frequency> <time>" pair in each line, which +will mean this CPU spent <time> usertime units of time at <frequency>. Output +will have one line for each of the supported frequencies. usertime units here +is 10mS (similar to other time exported in /proc). + +-------------------------------------------------------------------------------- +<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state +3600000 2089 +3400000 136 +3200000 34 +3000000 67 +2800000 172488 +-------------------------------------------------------------------------------- + + +- total_trans +This gives the total number of frequency transitions on this CPU. The cat +output will have a single count which is the total number of frequency +transitions. + +-------------------------------------------------------------------------------- +<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans +20 +-------------------------------------------------------------------------------- + +- trans_table +This will give a fine grained information about all the CPU frequency +transitions. The cat output here is a two dimensional matrix, where an entry +<i,j> (row i, column j) represents the count of number of transitions from +Freq_i to Freq_j. Freq_i is in descending order with increasing rows and +Freq_j is in descending order with increasing columns. The output here also +contains the actual freq values for each row and column for better readability. + +If the transition table is bigger than PAGE_SIZE, reading this will +return an -EFBIG error. + +-------------------------------------------------------------------------------- +<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table + From : To + : 3600000 3400000 3200000 3000000 2800000 + 3600000: 0 5 0 0 0 + 3400000: 4 0 2 0 0 + 3200000: 0 1 0 2 0 + 3000000: 0 0 1 0 3 + 2800000: 0 0 0 2 0 +-------------------------------------------------------------------------------- + + +3. Configuring cpufreq-stats + +To configure cpufreq-stats in your kernel +Config Main Menu + Power management options (ACPI, APM) ---> + CPU Frequency scaling ---> + [*] CPU Frequency scaling + [*] CPU frequency translation statistics + + +"CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure +cpufreq-stats. + +"CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the +statistics which includes time_in_state, total_trans and trans_table. + +Once this option is enabled and your CPU supports cpufrequency, you +will be able to see the CPU frequency statistics in /sysfs. |