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Where is "ondemand" governor?

asked 2014-04-02 06:49:58 -0500

netSys gravatar image

updated 2014-04-03 19:03:41 -0500

Hello folks,

Just I have problem searching ondemand governor on kernel. According to Fedora Power Management Guide, you can see what gov's kernel is using your machine with cpupower tool.

Ok, that's right. I run

# cpupower frequency-info

to get information about PM's CPU. This is result:

cpupower frequency-info analyzing CPU 0: driver: intel_pstate

CPUs which run at the same hardware frequency: 0

CPUs which need to have their frequency coordinated by software: 0

maximum transition latency: 0.97 ms.

hardware limits: 1.20 GHz - 3.10 GHz

available cpufreq governors: performance, powersave

current policy: frequency should be within 1.20 GHz and 3.10 GHz.

The governor "powersave" may decide which speed to use within this range.

current CPU frequency is 2.90 GHz (asserted by call to hardware).

boost state support:

Supported: yes Active: yes 2900 MHz max turbo 4 active cores 2900 MHz max turbo 3 active cores 2900 MHz max turbo 2 active cores 3100 MHz max turbo 1 active cores

Ok, Where is ondemand here? According to Fedora docs ondemand kernel is supported by default. However here is not supported. Avoid Power Management tools of Fedora, I decided to switch how to set "old" governor into the kernel with simple echo sintax. But still failed.

First of all,

 # cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors 
performance powersave

Fails, because does not allow set ondemand, bash returns failed when I tried assign ondemand into the kernel.

Anyway, I tried to load cpufreq_ondemand. This work because does not display any errors or debug.

I don't what happen here. However, I tried a Gentoo LiveCD that's supports "ondemand" profile for my CPU.

QA failed (?)

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answered 2014-04-03 06:44:17 -0500

joshuar gravatar image

It looks like you have a modern Intel CPU which automatically uses the intel_pstate kernel driver for scaling the CPU frequency and voltage. For this driver, the only two policies supported are performance and powersave. The traditional governor modules used by the acpi-cpufreq driver are not used by this driver.

Additionally, it looks like the cpupower tool is written solely for the acpi-cpufreq driver and so its output cannot be trusted when the intel_pstate driver is in use. I'd say the Fedora Power Management Guide needs to be updated too.

See this article for information about the original kernel patch introducing the driver. See also this Google+ discussion for reasons for using the intel_pstate driver over acpi-cpufreq.

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Asked: 2014-04-02 06:49:58 -0500

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Last updated: Apr 03 '14