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| CPU frequency and voltage scaling statictics in the Linux(TM) kernel |
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| L i n u x c p u f r e q - s t a t s d r i v e r |
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| - information for users - |
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| Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> |
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| Contents |
| 1. Introduction |
| 2. Statistics Provided (with example) |
| 3. Configuring cpufreq-stats |
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| 1. Introduction |
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| cpufreq-stats is a driver that provices CPU frequency statistics for each CPU. |
| This statistics is provided in /sysfs as a bunch of read_only interfaces. This |
| interface (when configured) will appear in a seperate directory under cpufreq |
| in /sysfs (<sysfs root>/devices/system/cpu/cpuX/cpufreq/stats/) for each CPU. |
| Various statistics will form read_only files under this directory. |
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| This driver is designed to be independent of any particular cpufreq_driver |
| that may be running on your CPU. So, it will work with any cpufreq_driver. |
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| 2. Statistics Provided (with example) |
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| cpufreq stats provides following statistics (explained in detail below). |
| - time_in_state |
| - total_trans |
| - trans_table |
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| All the statistics will be from the time the stats driver has been inserted |
| to the time when a read of a particular statistic is done. Obviously, stats |
| driver will not have any information about the frequency transitions before |
| the stats driver insertion. |
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| -------------------------------------------------------------------------------- |
| <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l |
| total 0 |
| drwxr-xr-x 2 root root 0 May 14 16:06 . |
| drwxr-xr-x 3 root root 0 May 14 15:58 .. |
| -r--r--r-- 1 root root 4096 May 14 16:06 time_in_state |
| -r--r--r-- 1 root root 4096 May 14 16:06 total_trans |
| -r--r--r-- 1 root root 4096 May 14 16:06 trans_table |
| -------------------------------------------------------------------------------- |
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| - time_in_state |
| This gives the amount of time spent in each of the frequencies supported by |
| this CPU. The cat output will have "<frequency> <time>" pair in each line, which |
| will mean this CPU spent <time> usertime units of time at <frequency>. Output |
| will have one line for each of the supported freuencies. usertime units here |
| is 10mS (similar to other time exported in /proc). |
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| -------------------------------------------------------------------------------- |
| <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state |
| 3600000 2089 |
| 3400000 136 |
| 3200000 34 |
| 3000000 67 |
| 2800000 172488 |
| -------------------------------------------------------------------------------- |
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| - total_trans |
| This gives the total number of frequency transitions on this CPU. The cat |
| output will have a single count which is the total number of frequency |
| transitions. |
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| -------------------------------------------------------------------------------- |
| <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans |
| 20 |
| -------------------------------------------------------------------------------- |
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| - trans_table |
| This will give a fine grained information about all the CPU frequency |
| transitions. The cat output here is a two dimensional matrix, where an entry |
| <i,j> (row i, column j) represents the count of number of transitions from |
| Freq_i to Freq_j. Freq_i is in descending order with increasing rows and |
| Freq_j is in descending order with increasing columns. The output here also |
| contains the actual freq values for each row and column for better readability. |
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| -------------------------------------------------------------------------------- |
| <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table |
| From : To |
| : 3600000 3400000 3200000 3000000 2800000 |
| 3600000: 0 5 0 0 0 |
| 3400000: 4 0 2 0 0 |
| 3200000: 0 1 0 2 0 |
| 3000000: 0 0 1 0 3 |
| 2800000: 0 0 0 2 0 |
| -------------------------------------------------------------------------------- |
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| 3. Configuring cpufreq-stats |
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| To configure cpufreq-stats in your kernel |
| Config Main Menu |
| Power management options (ACPI, APM) ---> |
| CPU Frequency scaling ---> |
| [*] CPU Frequency scaling |
| <*> CPU frequency translation statistics |
| [*] CPU frequency translation statistics details |
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| "CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure |
| cpufreq-stats. |
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| "CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the |
| basic statistics which includes time_in_state and total_trans. |
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| "CPU frequency translation statistics details" (CONFIG_CPU_FREQ_STAT_DETAILS) |
| provides fine grained cpufreq stats by trans_table. The reason for having a |
| seperate config option for trans_table is: |
| - trans_table goes against the traditional /sysfs rule of one value per |
| interface. It provides a whole bunch of value in a 2 dimensional matrix |
| form. |
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| Once these two options are enabled and your CPU supports cpufrequency, you |
| will be able to see the CPU frequency statistics in /sysfs. |
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