Kernel-3.10.0-957.el7_cpufreq-stats

published: updated: Kernel_3.10.0-957.el7_内核文档 
 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 (/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.

  1. 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.

:/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 “

:/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.

:/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.

:/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

  1. 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.

oosTech by Sam Lee