2 CPU frequency and voltage scaling statistics in the Linux(TM) kernel
5 L i n u x c p u f r e q - s t a t s d r i v e r
7 - information for users -
10 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
14 2. Statistics Provided (with example)
15 3. Configuring cpufreq-stats
20 cpufreq-stats is a driver that provides CPU frequency statistics for each CPU.
21 These statistics are provided in /sysfs as a bunch of read_only interfaces. This
22 interface (when configured) will appear in a separate directory under cpufreq
23 in /sysfs (<sysfs root>/devices/system/cpu/cpuX/cpufreq/stats/) for each CPU.
24 Various statistics will form read_only files under this directory.
26 This driver is designed to be independent of any particular cpufreq_driver
27 that may be running on your CPU. So, it will work with any cpufreq_driver.
30 2. Statistics Provided (with example)
32 cpufreq stats provides following statistics (explained in detail below).
37 All 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
39 statistic is done. Obviously, stats driver will not have any information
40 about the frequency transitions before the stats driver insertion.
42 --------------------------------------------------------------------------------
43 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l
45 drwxr-xr-x 2 root root 0 May 14 16:06 .
46 drwxr-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 --------------------------------------------------------------------------------
54 Write-only attribute that can be used to reset the stat counters. This can be
55 useful for evaluating system behaviour under different governors without the
59 This gives the amount of time spent in each of the frequencies supported by
60 this CPU. The cat output will have "<frequency> <time>" pair in each line, which
61 will mean this CPU spent <time> usertime units of time at <frequency>. Output
62 will have one line for each of the supported frequencies. usertime units here
63 is 10mS (similar to other time exported in /proc).
65 --------------------------------------------------------------------------------
66 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state
72 --------------------------------------------------------------------------------
76 This gives the total number of frequency transitions on this CPU. The cat
77 output will have a single count which is the total number of frequency
80 --------------------------------------------------------------------------------
81 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans
83 --------------------------------------------------------------------------------
86 This will give a fine grained information about all the CPU frequency
87 transitions. 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
89 Freq_i to Freq_j. Freq_i is in descending order with increasing rows and
90 Freq_j is in descending order with increasing columns. The output here also
91 contains the actual freq values for each row and column for better readability.
93 --------------------------------------------------------------------------------
94 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table
96 : 3600000 3400000 3200000 3000000 2800000
102 --------------------------------------------------------------------------------
105 3. Configuring cpufreq-stats
107 To configure cpufreq-stats in your kernel
109 Power management options (ACPI, APM) --->
110 CPU Frequency scaling --->
111 [*] CPU Frequency scaling
112 [*] CPU frequency translation statistics
115 "CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure
118 "CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the
119 statistics which includes time_in_state, total_trans and trans_table.
121 Once this option is enabled and your CPU supports cpufrequency, you
122 will be able to see the CPU frequency statistics in /sysfs.