Kernel-4.18.0-80.el8_cpufreq-stats

published: updated: Kernel_4.18.0-80.el8_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
(or the time the stats were reset) 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 ..
–w——- 1 root root 4096 May 14 16:06 reset
-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

  • reset
    Write-only attribute that can be used to reset the stat counters. This can be
    useful for evaluating system behaviour under different governors without the
    need for a reboot.

  • 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.

If the transition table is bigger than PAGE_SIZE, reading this will
return an -EFBIG error.

:/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 scaling” (CONFIG_CPU_FREQ) should be enabled to configure
cpufreq-stats.

“CPU frequency translation statistics” (CONFIG_CPU_FREQ_STAT) provides the
statistics which includes time_in_state, total_trans and trans_table.

Once this option is enabled and your CPU supports cpufrequency, you
will be able to see the CPU frequency statistics in /sysfs.

oosTech by Sam Lee