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2 CPU frequency and voltage scaling statictics in the Linux(TM) kernel
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5 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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7 - information for users -
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10 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
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12 Contents
13 1. Introduction
14 2. Statistics Provided (with example)
15 3. Configuring cpufreq-stats
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17
18 1. Introduction
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20 cpufreq-stats is a driver that provices CPU frequency statistics for each CPU.
21 This statistics is provided in /sysfs as a bunch of read_only interfaces. This
22 interface (when configured) will appear in a seperate 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.
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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.
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29
30 2. Statistics Provided (with example)
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32 cpufreq stats provides following statistics (explained in detail below).
33 - time_in_state
34 - total_trans
35 - trans_table
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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 freuencies. usertime units here
57 is 10mS (similar to other time exported in /proc).
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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.
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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 --------------------------------------------------------------------------------
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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
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110 "CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure
111 cpufreq-stats.
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113 "CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the
114 basic statistics which includes time_in_state and total_trans.
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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 seperate 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.
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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.
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