linux-kernel - Re: [RFC v2 0/3][TESTS] LAB: Support for Legacy Application Booster governor

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Date:	Fri, 24 May 2013 14:21:30 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Lukasz Majewski <l.majewski@...sung.com>
Cc:	Jonghwa Lee <jonghwa3.lee@...sung.com>,
	"Rafael J. Wysocky" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
	Vicent Guittot <vincent.guittot@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Lukasz Majewski <l.majewski@...ess.pl>
Subject: Re: [RFC v2 0/3][TESTS] LAB: Support for Legacy Application Booster
 governor - tests results

On 24 May 2013 14:00, Lukasz Majewski <l.majewski@...sung.com> wrote:
> The overclock frequency (1.5 GHz) is possible to set as an ordinary,
> available frequency (policy->max) for ondemand.
>
> Unfortunately with our load patterns, this frequency rapidly increases
> internal chip temperature (chip goes out of available power/thermal
> dissipation range), and consumes extra power when not needed.
>
> The core idea with overclock is to increase ("boost") the frequency
> when conditions allow to do it (for example load is affined to a single
> core, other are idle). Then we will not exceed power/thermal budget, but
> increase performance (and even save power).
>
>
> Overclocking is efficiently utilized by LAB, which relies on a number of
> idle cpus. Thus, we can easily asses if we can enable it.
>
> I also foresee potential use of overclocking, when scheduler will take a
> major role of power saver for mobile (ARM) linux. Since it will try to
> pack as much tasks as possible to a single core - it will need a
> framework/API to "boost" their execution.

Okay.. so its exactly what I thought the reason would be.

What I would have done if I was in your place is:

Add following sysfs tunables to ondemand governor:

- overdrive_freq: We will go over this frequency only when
number of busy cores is <= overdrive_cores..
For your case it will be 1.4 GHz

- overdrive_cores: We will enable overdrive frequencies only if no. of
busy cores is <= overdrive_cores. Zero by default (So, that this feature
is disabled by default) and 1 for your case.

And your driver will include all the available frequencies in the freq
table.

I hope this will be the most generic solution to your problem..

What do you say?

--
viresh
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