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

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Date:	Mon, 27 May 2013 09:34:55 +0200
From:	Lukasz Majewski <l.majewski@...sung.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
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

Hi Viresh,

> On 24 May 2013 16:50, Lukasz Majewski <l.majewski@...sung.com> wrote:
> >> On 24 May 2013 14:00, Lukasz Majewski <l.majewski@...sung.com>
> >> wrote:
> 
> > This is not safe IMHO to add permanently overclocked frequency to
> > the freq table. Since, for example, thermal framework also asks for
> > reference to this table.
> 
> Yes, its wrong. Even adding it permanently this way would be a problem
> if governor is changed to performance. :)
> 
> > The idea beneath overclocking is to add "dangerous" frequency to the
> > frequency table only when necessary (and remove it when not needed).
> 
> Hmm.. probably the idea beneath is to use dangerous frequency only
> when we are assured that we will not break system.. 

Exactly, this is the idea.

> It doesn't have
> anything to do with cpufreq table entries :)
> 
> > In this way, the thermal framework (as it is done at our platform)
> > will decrease the frequency (according to thermal governor :-) ) to
> > safe level.
> >
> > Overclocking is disabled in 2 ways (at our setup):
> > - thermal framework is here to help us
> > - lab governor disables the overclocking when favorable conditions
> > are gone.
> 
> I don't want to discuss OR think about LAB for now.. Want to get
> overclocking feature in first.
> 
> > One more remark - enabling tb_en_over_clk at sysfs (echo 1
> >> /sys/devices/system/cpu/cpu0/cpufreq/tb_en_over_clk)
> > adds overclock frequency to frequency table and updates policy.
> 
> What if it is enabled and governor is changed to performance
> without disabling it... Who will take care of disabling dangerous
> frequencies?

So we could disable overclocking by default when policy is changed, or
when we remove governor (at cpufreq_unregister_governor()).

> 
> One thing I am certain about is to make overclocking a generic and
> core feature, rather than platform specific...

Ok, I see your point. I will prepare appropriate patches to rewrite
overclocking as a generic framework.

> 
> What about adding overdrive frequencies in freq table permanently
> but with .index field as: CPUFREQ_ENTRY_OVERDRIVE ??
> 
> This way we will use frequencies marked with
> CPUFREQ_ENTRY_OVERDRIVE only when we have overclocking
> enabled. And not at other times?

It seems to be a good idea. In this way we could solve some other
problems as well (like specifying not single overclocked frequency,
make sysfs entries read only).

As I've stated above, I will prepare only overclocking patches, with
new generic approach.



-- 
Best regards,

Lukasz Majewski

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