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+ CPU frequency and voltage scaling statictics in the Linux(TM) kernel
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+
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+
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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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+
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+ - information for users -
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+
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+
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+ Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
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+
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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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+
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+
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+1. Introduction
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+
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+cpufreq-stats is a driver that provices CPU frequency statistics for each CPU.
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+This statistics is provided in /sysfs as a bunch of read_only interfaces. This
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+interface (when configured) will appear in a seperate 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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+
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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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+
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+
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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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+
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+All the statistics will be from the time the stats driver has been inserted
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+to the time when a read of a particular statistic is done. Obviously, stats
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+driver will not have any information about the the frequcny transitions before
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+the stats driver insertion.
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+
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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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+-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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+--------------------------------------------------------------------------------
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+
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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 freuencies. usertime units here
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+is 10mS (similar to other time exported in /proc).
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+
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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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+--------------------------------------------------------------------------------
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+
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+
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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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+--------------------------------------------------------------------------------
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+<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans
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+20
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+--------------------------------------------------------------------------------
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+
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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 is in descending order with increasing rows and
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+Freq_j is in descending order with increasing columns. The output here also
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+contains the actual freq values for each row and column for better readability.
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+
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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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+--------------------------------------------------------------------------------
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+
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+
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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 translation statistics details
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+
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+
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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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+
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+"CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the
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+basic statistics which includes time_in_state and total_trans.
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+
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+"CPU frequency translation statistics details" (CONFIG_CPU_FREQ_STAT_DETAILS)
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+provides fine grained cpufreq stats by trans_table. The reason for having a
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+seperate config option for trans_table is:
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+- trans_table goes against the traditional /sysfs rule of one value per
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+ interface. It provides a whole bunch of value in a 2 dimensional matrix
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+ form.
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+
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+Once these two options are 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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+
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+
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+
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+
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Venkatesh Pallipadi