Venkatesh Pallipadi | 21e3024 | 2005-05-25 14:43:56 -0700 | [diff] [blame] | 1 | |
| 2 | CPU frequency and voltage scaling statictics 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 | |
| 12 | Contents |
| 13 | 1. Introduction |
| 14 | 2. Statistics Provided (with example) |
| 15 | 3. Configuring cpufreq-stats |
| 16 | |
| 17 | |
| 18 | 1. Introduction |
| 19 | |
| 20 | cpufreq-stats is a driver that provices CPU frequency statistics for each CPU. |
| 21 | This statistics is provided in /sysfs as a bunch of read_only interfaces. This |
| 22 | interface (when configured) will appear in a seperate 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. |
| 25 | |
| 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. |
| 28 | |
| 29 | |
| 30 | 2. Statistics Provided (with example) |
| 31 | |
| 32 | cpufreq stats provides following statistics (explained in detail below). |
| 33 | - time_in_state |
| 34 | - total_trans |
| 35 | - trans_table |
| 36 | |
| 37 | All the statistics will be from the time the stats driver has been inserted |
| 38 | to the time when a read of a particular statistic is done. Obviously, stats |
Tobias Klauser | d533f67 | 2005-09-10 00:26:46 -0700 | [diff] [blame^] | 39 | driver will not have any information about the frequency transitions before |
Venkatesh Pallipadi | 21e3024 | 2005-05-25 14:43:56 -0700 | [diff] [blame] | 40 | the stats driver insertion. |
| 41 | |
| 42 | -------------------------------------------------------------------------------- |
| 43 | <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l |
| 44 | total 0 |
| 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 | -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 |
| 53 | This gives the amount of time spent in each of the frequencies supported by |
| 54 | this CPU. The cat output will have "<frequency> <time>" pair in each line, which |
| 55 | will mean this CPU spent <time> usertime units of time at <frequency>. Output |
| 56 | will have one line for each of the supported freuencies. usertime units here |
| 57 | is 10mS (similar to other time exported in /proc). |
| 58 | |
| 59 | -------------------------------------------------------------------------------- |
| 60 | <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state |
| 61 | 3600000 2089 |
| 62 | 3400000 136 |
| 63 | 3200000 34 |
| 64 | 3000000 67 |
| 65 | 2800000 172488 |
| 66 | -------------------------------------------------------------------------------- |
| 67 | |
| 68 | |
| 69 | - total_trans |
| 70 | This gives the total number of frequency transitions on this CPU. The cat |
| 71 | output will have a single count which is the total number of frequency |
| 72 | transitions. |
| 73 | |
| 74 | -------------------------------------------------------------------------------- |
| 75 | <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans |
| 76 | 20 |
| 77 | -------------------------------------------------------------------------------- |
| 78 | |
| 79 | - trans_table |
| 80 | This will give a fine grained information about all the CPU frequency |
| 81 | transitions. 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 |
| 83 | Freq_i to Freq_j. Freq_i is in descending order with increasing rows and |
| 84 | Freq_j is in descending order with increasing columns. The output here also |
| 85 | contains 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 | |
| 99 | 3. Configuring cpufreq-stats |
| 100 | |
| 101 | To configure cpufreq-stats in your kernel |
| 102 | Config 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 |
| 111 | cpufreq-stats. |
| 112 | |
| 113 | "CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the |
| 114 | basic statistics which includes time_in_state and total_trans. |
| 115 | |
| 116 | "CPU frequency translation statistics details" (CONFIG_CPU_FREQ_STAT_DETAILS) |
| 117 | provides fine grained cpufreq stats by trans_table. The reason for having a |
| 118 | seperate 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 | |
| 123 | Once these two options are enabled and your CPU supports cpufrequency, you |
| 124 | will be able to see the CPU frequency statistics in /sysfs. |
| 125 | |
| 126 | |
| 127 | |
| 128 | |