linux-kernel - Re: [PATCH] cpufreq: ondemand: Introduces stepped frequency increase

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Message-ID: <20090709233447.GA1770@ucw.cz>
Date:	Fri, 10 Jul 2009 01:34:47 +0200
From:	Pavel Machek <pavel@....cz>
To:	Corrado Zoccolo <czoccolo@...il.com>
Cc:	Matthew Garrett <mjg@...hat.com>, Dave Jones <davej@...hat.com>,
	linux-kernel@...r.kernel.org, cpufreq@...r.kernel.org
Subject: Re: [PATCH] cpufreq: ondemand: Introduces stepped frequency
	increase

On Wed 2009-07-08 19:41:23, Corrado Zoccolo wrote:
> Hi Matthew,
> 
> On Wed, Jul 8, 2009 at 6:10 PM, Matthew Garrett<mjg@...hat.com> wrote:
> > On Wed, Jul 08, 2009 at 03:56:33PM +0200, Corrado Zoccolo wrote:
> >> The patch introduces a new sysfs tunable cpufreq/ondemand/freq_step,
> >> as found in conservative governor, to chose the frequency increase step,
> >> expressed as percentage (default = 100 is previous behaviour).
> >>
> >> This allows fine tuning powersaving on mobile CPUs, since smaller steps will allow to:
> >> * absorb punctual load spikes
> >> * stabilize at the needed frequency, without passing for more power consuming states, and
> >
> > Is this a measured powersaving? The ondemand model is based on the
> > assumption that the idle state is disproportionately lower in power than
> > any running state, and therefore it's more sensible to run flat out for
> > short periods of time than run at half speed for longer. Is this
> > inherently flawed, or is it an artifact of differences in your processor
> > design?

Different processors behave differently -- that assumption is wrong at
least for old athlon64s... Those have power-hungry idle states, and 4x
power consumption at 2x frequency....

(Original Intel speedstep was similar iirc).

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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