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Documentation / cpu-freq / cpufreq-stats.txt




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Based on kernel version 3.16. Page generated on 2014-08-06 21:36 EST.

1	
2	     CPU frequency and voltage scaling statistics 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 provides CPU frequency statistics for each CPU.
21	These statistics are provided in /sysfs as a bunch of read_only interfaces. This
22	interface (when configured) will appear in a separate 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 
39	driver will not have any information about the frequency transitions before
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 frequencies. 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	separate 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	
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