Documentation / cpu-freq / cpufreq-stats.txt

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Based on kernel version 3.9. Page generated on 2013-05-02 22:56 EST.

	
	     CPU frequency and voltage scaling statistics in the Linux(TM) kernel
	
	
	             L i n u x    c p u f r e q - s t a t s   d r i v e r
	
	                       - information for users -
	
	
	             Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
	
	Contents
	1. Introduction
	2. Statistics Provided (with example)
	3. Configuring cpufreq-stats
	
	
	1. Introduction
	
	cpufreq-stats is a driver that provides CPU frequency statistics for each CPU.
	These statistics are provided in /sysfs as a bunch of read_only interfaces. This
	interface (when configured) will appear in a separate 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.
	
	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.
	
	
	2. Statistics Provided (with example)
	
	cpufreq stats provides following statistics (explained in detail below).
	-  time_in_state
	-  total_trans
	-  trans_table
	
	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.
	
	--------------------------------------------------------------------------------
	<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
	--------------------------------------------------------------------------------
	
	-  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 frequencies. usertime units here 
	is 10mS (similar to other time exported in /proc).
	
	--------------------------------------------------------------------------------
	<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat time_in_state 
	3600000 2089
	3400000 136
	3200000 34
	3000000 67
	2800000 172488
	--------------------------------------------------------------------------------
	
	
	-  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.
	
	--------------------------------------------------------------------------------
	<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat total_trans
	20
	--------------------------------------------------------------------------------
	
	-  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.
	
	--------------------------------------------------------------------------------
	<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 
	--------------------------------------------------------------------------------
	
	
	3. Configuring cpufreq-stats
	
	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
	
	
	"CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure
	cpufreq-stats.
	
	"CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the
	basic statistics which includes time_in_state and total_trans.
	
	"CPU frequency translation statistics details" (CONFIG_CPU_FREQ_STAT_DETAILS)
	provides fine grained cpufreq stats by trans_table. The reason for having a
	separate 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.
	
	Once these two options are enabled and your CPU supports cpufrequency, you
	will be able to see the CPU frequency statistics in /sysfs.
	
	
	

• [ cpu-freq ]
• amd-powernow.txt
• boost.txt
• core.txt
• cpu-drivers.txt
• cpufreq-nforce2.txt
• cpufreq-stats.txt
• governors.txt
• index.txt
• pcc-cpufreq.txt
• user-guide.txt
•