cpufreq-stats.rst (4598B)
1.. SPDX-License-Identifier: GPL-2.0 2 3========================================== 4General Description of sysfs CPUFreq Stats 5========================================== 6 7information for users 8 9 10Author: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> 11 12.. Contents 13 14 1. Introduction 15 2. Statistics Provided (with example) 16 3. Configuring cpufreq-stats 17 18 191. Introduction 20=============== 21 22cpufreq-stats is a driver that provides CPU frequency statistics for each CPU. 23These statistics are provided in /sysfs as a bunch of read_only interfaces. This 24interface (when configured) will appear in a separate directory under cpufreq 25in /sysfs (<sysfs root>/devices/system/cpu/cpuX/cpufreq/stats/) for each CPU. 26Various statistics will form read_only files under this directory. 27 28This driver is designed to be independent of any particular cpufreq_driver 29that may be running on your CPU. So, it will work with any cpufreq_driver. 30 31 322. Statistics Provided (with example) 33===================================== 34 35cpufreq stats provides following statistics (explained in detail below). 36 37- time_in_state 38- total_trans 39- trans_table 40 41All the statistics will be from the time the stats driver has been inserted 42(or the time the stats were reset) to the time when a read of a particular 43statistic is done. Obviously, stats driver will not have any information 44about the frequency transitions before the stats driver insertion. 45 46:: 47 48 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l 49 total 0 50 drwxr-xr-x 2 root root 0 May 14 16:06 . 51 drwxr-xr-x 3 root root 0 May 14 15:58 .. 52 --w------- 1 root root 4096 May 14 16:06 reset 53 -r--r--r-- 1 root root 4096 May 14 16:06 time_in_state 54 -r--r--r-- 1 root root 4096 May 14 16:06 total_trans 55 -r--r--r-- 1 root root 4096 May 14 16:06 trans_table 56 57- **reset** 58 59Write-only attribute that can be used to reset the stat counters. This can be 60useful for evaluating system behaviour under different governors without the 61need for a reboot. 62 63- **time_in_state** 64 65This gives the amount of time spent in each of the frequencies supported by 66this CPU. The cat output will have "<frequency> <time>" pair in each line, which 67will mean this CPU spent <time> usertime units of time at <frequency>. Output 68will have one line for each of the supported frequencies. usertime units here 69is 10mS (similar to other time exported in /proc). 70 71:: 72 73 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state 74 3600000 2089 75 3400000 136 76 3200000 34 77 3000000 67 78 2800000 172488 79 80 81- **total_trans** 82 83This gives the total number of frequency transitions on this CPU. The cat 84output will have a single count which is the total number of frequency 85transitions. 86 87:: 88 89 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans 90 20 91 92- **trans_table** 93 94This will give a fine grained information about all the CPU frequency 95transitions. The cat output here is a two dimensional matrix, where an entry 96<i,j> (row i, column j) represents the count of number of transitions from 97Freq_i to Freq_j. Freq_i rows and Freq_j columns follow the sorting order in 98which the driver has provided the frequency table initially to the cpufreq core 99and so can be sorted (ascending or descending) or unsorted. The output here 100also contains the actual freq values for each row and column for better 101readability. 102 103If the transition table is bigger than PAGE_SIZE, reading this will 104return an -EFBIG error. 105 106:: 107 108 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table 109 From : To 110 : 3600000 3400000 3200000 3000000 2800000 111 3600000: 0 5 0 0 0 112 3400000: 4 0 2 0 0 113 3200000: 0 1 0 2 0 114 3000000: 0 0 1 0 3 115 2800000: 0 0 0 2 0 116 1173. Configuring cpufreq-stats 118============================ 119 120To configure cpufreq-stats in your kernel:: 121 122 Config Main Menu 123 Power management options (ACPI, APM) ---> 124 CPU Frequency scaling ---> 125 [*] CPU Frequency scaling 126 [*] CPU frequency translation statistics 127 128 129"CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure 130cpufreq-stats. 131 132"CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the 133statistics which includes time_in_state, total_trans and trans_table. 134 135Once this option is enabled and your CPU supports cpufrequency, you 136will be able to see the CPU frequency statistics in /sysfs.