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136 lines
4.5 KiB
136 lines
4.5 KiB
.. SPDX-License-Identifier: GPL-2.0 |
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========================================== |
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General Description of sysfs CPUFreq Stats |
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========================================== |
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information for users |
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Author: Venkatesh Pallipadi <[email protected]> |
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.. Contents |
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1. Introduction |
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2. Statistics Provided (with example) |
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3. Configuring cpufreq-stats |
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1. Introduction |
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=============== |
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cpufreq-stats is a driver that provides CPU frequency statistics for each CPU. |
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These statistics are provided in /sysfs as a bunch of read_only interfaces. This |
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interface (when configured) will appear in a separate directory under cpufreq |
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in /sysfs (<sysfs root>/devices/system/cpu/cpuX/cpufreq/stats/) for each CPU. |
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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 |
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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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===================================== |
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cpufreq stats provides following statistics (explained in detail below). |
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- time_in_state |
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- total_trans |
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- trans_table |
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All the statistics will be from the time the stats driver has been inserted |
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(or the time the stats were reset) to the time when a read of a particular |
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statistic is done. Obviously, stats driver will not have any information |
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about the frequency transitions before the stats driver insertion. |
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:: |
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<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l |
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total 0 |
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drwxr-xr-x 2 root root 0 May 14 16:06 . |
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drwxr-xr-x 3 root root 0 May 14 15:58 .. |
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--w------- 1 root root 4096 May 14 16:06 reset |
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-r--r--r-- 1 root root 4096 May 14 16:06 time_in_state |
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-r--r--r-- 1 root root 4096 May 14 16:06 total_trans |
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-r--r--r-- 1 root root 4096 May 14 16:06 trans_table |
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- **reset** |
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Write-only attribute that can be used to reset the stat counters. This can be |
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useful for evaluating system behaviour under different governors without the |
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need for a reboot. |
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- **time_in_state** |
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This gives the amount of time spent in each of the frequencies supported by |
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this CPU. The cat output will have "<frequency> <time>" pair in each line, which |
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will mean this CPU spent <time> usertime units of time at <frequency>. Output |
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will have one line for each of the supported frequencies. usertime units here |
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is 10mS (similar to other time exported in /proc). |
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:: |
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<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state |
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3600000 2089 |
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3400000 136 |
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3200000 34 |
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3000000 67 |
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2800000 172488 |
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- **total_trans** |
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This gives the total number of frequency transitions on this CPU. The cat |
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output will have a single count which is the total number of frequency |
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transitions. |
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:: |
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<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans |
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20 |
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- **trans_table** |
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This will give a fine grained information about all the CPU frequency |
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transitions. The cat output here is a two dimensional matrix, where an entry |
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<i,j> (row i, column j) represents the count of number of transitions from |
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Freq_i to Freq_j. Freq_i rows and Freq_j columns follow the sorting order in |
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which the driver has provided the frequency table initially to the cpufreq core |
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and so can be sorted (ascending or descending) or unsorted. The output here |
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also contains the actual freq values for each row and column for better |
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readability. |
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If the transition table is bigger than PAGE_SIZE, reading this will |
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return an -EFBIG error. |
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:: |
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<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table |
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From : To |
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: 3600000 3400000 3200000 3000000 2800000 |
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3600000: 0 5 0 0 0 |
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3400000: 4 0 2 0 0 |
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3200000: 0 1 0 2 0 |
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3000000: 0 0 1 0 3 |
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2800000: 0 0 0 2 0 |
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3. Configuring cpufreq-stats |
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============================ |
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To configure cpufreq-stats in your kernel:: |
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Config Main Menu |
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Power management options (ACPI, APM) ---> |
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CPU Frequency scaling ---> |
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[*] CPU Frequency scaling |
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[*] CPU frequency translation statistics |
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"CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure |
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cpufreq-stats. |
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"CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the |
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statistics which includes time_in_state, total_trans and trans_table. |
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Once this option is enabled and your CPU supports cpufrequency, you |
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will be able to see the CPU frequency statistics in /sysfs.
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