linux-kernel - Re: [PATCH v3 1/3] cpufreq: Add boost frequency support in core

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Date:	Tue, 18 Jun 2013 11:12:36 +0200
From:	Lukasz Majewski <l.majewski@...sung.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	"Rafael J. Wysocky" <rjw@...k.pl>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Jonghwa Lee <jonghwa3.lee@...sung.com>,
	Myungjoo Ham <myungjoo.ham@...sung.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Lukasz Majewski <l.majewski@...ess.pl>,
	Andre Przywara <andre.przywara@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Amit Daniel Kachhap <amit.daniel@...sung.com>
Subject: Re: [PATCH v3 1/3] cpufreq: Add boost frequency support in core

On Tue, 18 Jun 2013 14:10:28 +0530, Viresh Kumar wrote:
> On 18 June 2013 13:54, Lukasz Majewski <l.majewski@...sung.com> wrote:
> > On Tue, 18 Jun 2013 08:42:13 +0200, Viresh Kumar wrote:
> 
> >> Its not about how long.. One cpu type can work longer with boost
> >> freq compared to other.
> >>
> >> What we probably need is:
> >> - Enabled boost from sysfs if required (now below steps will come
> >> into picture)
> >> - See how many cpus are running, if only one then start using boost
> >> freqs
> >
> > You are right here.
> >
> > I'd like to propose following solution:
> > 1. For acpi (where boost_enable come into play) - do not consider
> > number of active cpus (this is done in HW anyway)
> >
> > 2. For SW solution evaluate how many CPUs are running. If only one
> > is running then allow enabling boost from sysfs.
> 
> Looks fine.

Ok,

> 
> > But following situation is also possible: User enable boost when one
> > core is only running and then for some reason other core is woken
> > up. What shall be done then?
> > Shall we then disable boost immediately when cpufreq detects that
> > more than one core is running? Or leave this situation to be
> > handled by thermal subsystem?
> 
> Obviously disable boost ASAP. Every SoC might not have a thermal
> framework glue to do it.

Implementation of counting number of idle CPUs would impose extending
the cpufreq core itself. Do you have any hints how this can be done in
a neat way?

I suspect, that porting the LAB solution to the cpufreq core may be not
easy. I think that the best place for it would be governor core code.

> 
> > As a side note:
> > Logic proposed at point 2, is already implemented at LAB
> > (enable LAB only when one core is running and disable it when more
> > than one come into play).
> 
> Hmm.. So, eventually that will go away now :)

But this is not the only functionality, which LAB posses :-).

> 
> >> - Now thermal should be come into picture to save chip in case a
> >> single cpu running at boost can burn it out.
> >
> > I will extent v4 to embrace code which switches off boost at
> > thermal.
> 
> Gud.

Ok.

-- 
Best regards,

Lukasz Majewski

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