Re: cpuidle governors

[Daniel Lezcano <daniel.lezcano@linaro.org>]

On 11/07/2013 02:44 PM, Jean Delvare wrote:
> Hi all,
>
> I had to work on cpuidle recently and there are two things which caused
> me trouble and I'd like to discuss.
>
> 1* Is there no documentation about how the available governors (menu and
> ladder) work? I found good documentation of the general architecture and
> API in Documentation/cpuidle, but I am missing a description of the
> internal logic of each available governor (just like
> Documentation/cpu-freq/governors.txt for cpufreq.)

IMO, the code review and the header description in the menu.c file is 
the best way to understand how the governor works. For very specific 
questions, try asking in the mailing list.

> Also, the
> documentation says that "the kernel picks the best governor based on
> governor ratings" but that's pretty vague. An explanation of how the
> governors are rated would be good to have. Could this be added?

Yeah, actually they are rated but depending on the system configuration 
one fit better than the other one. Tickless system => menu governor, 
Periodic system => ladder governor. Using a tickless system with the 
ladder governor is less efficient from a power saving POV.

> 2* Is there no way to specify/force the cpuidle governor at boot time? I
> found the cpuidle_sysfs_switch parameter and then I can change the
> governor in sysfs, but this seems overly complicated (and apparently
> discouraged) in a production environment. Wouldn't it be easier to
> implement a cpuidle.governor=xxx boot parameter? That way we don't have
> to deal with run-time changes, but the user can still force a specific
> governor.

Yes, that may make sense.

Thanks
   -- Daniel


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