System information

Power Management 139

/sys/devices/system/cpu/. If you list the contents of this directory, you will

find a cpu{0..x} subdirectory for each processor, and several other files and direc-

tories. A cpufreq subdirectory in each processor directory holds a number of files

and directories that define the parameters for CPUfreq. Some of them are writable

(for root), some of them are read-only. If your system currently uses the on-demand

or conservative governor, you will see a separate subdirectory for those governors in

cpufreq, containing the parameters for the governors.

NOTE: Different Processor Settings

The settings under the cpufreq directory can be different for each proces-

sor. If you want to use the same policies across all processors, you need

to adjust the parameters for each processor. Instead of looking up or mod-

ifying the current settings manually (in /sys/devices/system/cpu*/

cpufreq), we advise to use the tools provided by the cpupower package

or by the older cpufrequtils package for that.

11.3 Viewing, Monitoring and

Tuning Power-related Settings

The following command line tools are available for that purpose:

Using the cpufrequtils Tools (page140)

With the tools of the cpufrequtils package you can view and modify set-

tings of the kernel-related CPUfreq subsystem. The cpufreq* commands are

useful for modifying settings related to P-states, especially frequency scaling and

CPUfreq governors.

Using the cpupower Tools (page141)

The new cpupower tool was designed to give an overview of all CPU power-re-

lated parameters that are supported on a given machine, including turbo (or boost)

states. Use the tool set to view and modify settings of the kernel-related CPUfreq

and cpuidle systems as well as other settings not related to frequency scaling or

idle states. The integrated monitoring framework can access both Kernel-relat-

ed parameters and hardware statistics and is thus ideally suited for performance

benchmarks. It also helps you to identify the dependencies between turbo and idle

states.