linux-kernel - Re: [PATCH 7/7] ondemand: Solve the big performance issue with ondemand during disk IO

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Date:	Tue, 27 Apr 2010 15:01:39 +0200
From:	Pavel Machek <pavel@....cz>
To:	Mike Chan <mike@...roid.com>
Cc:	Thomas Renninger <trenn@...e.de>,
	Arjan van de Ven <arjan@...radead.org>,
	?ric Piel <eric.piel@...mplin-utc.net>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	mingo@...e.hu, peterz@...radead.org, tglx@...utronix.de,
	davej@...hat.com, cpufreq@...r.kernel.org
Subject: Re: [PATCH 7/7] ondemand: Solve the big performance issue with
 ondemand during disk IO

Hi!

> > But I follow Eric and agree that if it costs that much, changing
> > above sounds sane.
> > Still, I could imagine some people might want to not raise freq on IO bound
> > process activity, therefore this should get another ondemand param, similar
> > to ignore_nice_load.
> >
> 
> I agree with Thomas here. Some of these assumptions on IO / FSB
> performance with cpu speed do not hold true on various ARM platforms.
> 
> Perhaps we could have a min_io_freq value? Which is the min speed for
> the cpu to run at for IO bound activity. In the original patch,
> min_io_freq = scaling_max_freq. For various arm devices I can happily
> set min_io_freq to the lowest cpu speed that satisfies bus speeds.

'satisfies bus speeds' == minimum cpu frequency where i/o works at all

 or

 == minimum cpu frequency where i/o works at full speed

?
								Pavel

-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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