1 2 CPU frequency and voltage scaling statistics in the Linux(TM) kernel 3 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 93-------------------------------------------------------------------------------- 94<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table 95 From : To 96 : 3600000 3400000 3200000 3000000 2800000 97 3600000: 0 5 0 0 0 98 3400000: 4 0 2 0 0 99 3200000: 0 1 0 2 0 100 3000000: 0 0 1 0 3 101 2800000: 0 0 0 2 0 102-------------------------------------------------------------------------------- 103 104 1053. Configuring cpufreq-stats 106 107To configure cpufreq-stats in your kernel 108Config Main Menu 109 Power management options (ACPI, APM) ---> 110 CPU Frequency scaling ---> 111 [*] CPU Frequency scaling 112 [*] CPU frequency translation statistics 113 114 115"CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure 116cpufreq-stats. 117 118"CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the 119statistics which includes time_in_state, total_trans and trans_table. 120 121Once this option is enabled and your CPU supports cpufrequency, you 122will be able to see the CPU frequency statistics in /sysfs. 123