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

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Date:	Fri, 24 May 2013 13:34:42 +0200
From:	Lukasz Majewski <l.majewski@...sung.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	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>,
	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

Hi Viresh,

> On 24 May 2013 14:36, Daniel Lezcano <daniel.lezcano@...aro.org>
> wrote:
> > I agree with Viresh, a new governor is not necessary here for that.
> 
> Their patchset had two parts.. One is LAB and other is overclocking.
> We are trying to solve overclocking for which they never wanted a
> new governor. :)

Overclocking can be uses as a standalone feature. However it is crucial
for effective LAB operation.

> 
> > There is the /sys/devices/system/cpufreq/boost option existing for
> > x86 platform, why do not reuse it ? It is supposed to do exactly
> > what you want to achieve.
> 
> The problem is that it was added at the wrong place.. It should have
> been at cpu/cpuX/cpufreq/boost...
> 
> Consider how will we achieve it for big LITTLE.. We know we can
> go to overdrive only for a single core in big but for two cores in
> LITTLE at the same time.. So, we need that in the location I just
> mentioned...

I think that power/thermal envelope here is a key. We can overclock as
many cores as we want if we don't exceed limits :-)

Scheduler assignment of tasks to cores and core type decision on which
it would run is a different story for b.L. 

> 
> Over that.. I believe it is governor specific too.. It shouldn't be
> part of conservative as it should be conservative rather then
> aggressive :)
> 
> > IMO, the logic of boosting one core when the other are idle should
> > be in the driver itself and certainly not setup by the user, except
> > if we consider acceptable the user can burn its board ... :)

Sysfs entry can be read only and governor code can be responsible for
enabling overclocking.

Overclocking patch provides API implemented at cpufreq.h file to allow
in-kernel overclocking.

> 
> I didn't get it completely.. So, with the options I gave user can only
> say.. boost if required and only when few cores are active. User
> can't just set max freq continuously if he wishes..



-- 
Best regards,

Lukasz Majewski

Samsung R&D Poland (SRPOL) | Linux Platform Group
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