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

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Date:	Fri, 24 May 2013 12:28:40 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	Lukasz Majewski <l.majewski@...sung.com>,
	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

On 05/24/2013 11:13 AM, Viresh Kumar wrote:
> 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. :)
> 
>> 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...

Yes, I saw in the commit log (615b7300717b9ad5c23d1f391843484fe30f6c12),
that should be done.

> 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 thought the constraints should be hardcoded in the driver and only one
option is exposed to the userspace. If the user sets
ondemand|performance + boost, then the exynos's or b.L's drivers know
when they can go to boost (1x core, 1x big core, 2x little core, ...).

> Over that.. I believe it is governor specific too.. It shouldn't be part
> of conservative as it should be conservative rather then aggressive :)

Yes, it is part of the governor policy and maybe that could fall in the
common cpufreq framework.

>> 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 ... :)
> 
> 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..

Ok, may be I misunderstood. You suggested to define 'overdrive_cores'
where the user can setup when to overdrive a core. If the user set an
incorrect value, IIUC, the thermal value can go beyond the thermal limit
and break the board. I am just worried this option is dangerous.




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