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diff --git a/Documentation/cpu-freq/cpufreq-stats.rst b/Documentation/cpu-freq/cpufreq-stats.rst new file mode 100644 index 000000000..9ad695b1c --- /dev/null +++ b/Documentation/cpu-freq/cpufreq-stats.rst @@ -0,0 +1,136 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========================================== +General Description of sysfs CPUFreq Stats +========================================== + +information for users + + +Author: 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 rows and Freq_j columns follow the sorting order in +which the driver has provided the frequency table initially to the cpufreq core +and so can be sorted (ascending or descending) or unsorted. 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. |