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21e3024c VP |
1 | |
2 | CPU frequency and voltage scaling statictics 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 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. | |
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 | |
d533f671 | 39 | driver will not have any information about the frequency transitions before |
21e3024c VP |
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). | |
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 | 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. | |
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 | ||
128 |