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 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. 125 126 127 128 129