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From: Thomas Renninger <trenn@suse.de>
Organization: SUSE Products GmbH
To: Arjan van de Ven <arjan@infradead.org>
Subject: Re: [PATCH 7/7] ondemand: Solve the big performance issue with ondemand during disk IO
Date: Tue, 20 Apr 2010 11:24:00 +0200
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On Monday 19 April 2010 15:43:25 Arjan van de Ven wrote:
> On Mon, 19 Apr 2010 10:29:47 +0200
> Éric Piel <eric.piel@tremplin-utc.net> wrote:
> > > 
> > > The problem and fix are both verified with the "perf timechar" tool.
> > Hi,
> > I don't doubt that keeping the cpu full frequency during IO can
> > improve some specific workloads, however in your log message you
> > don't explain how much we are loosing.
> 
> first of all, it's so bad that people will just turn the whole power
> management off... at which point fixing the really bad bug is actually
> quite a win
Not sure you fix a bug, I expect this was done on purpose.
The ondemand governor disadvantages processes with alternating short CPU
load peaks and idle sequences.
IO bound processes typically show up with such a behavior.

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.

    Thomas