linux-kernel - Re: [PATCH v2] cpuidle: Fix the menu governor to boost IO performance

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Date:	Tue, 15 Sep 2009 06:15:12 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, lenb@...nel.org, mingo@...e.hu,
	yanmin_zhang@...ux.intel.com, jens.axboe@...cle.com,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>
Subject: Re: [PATCH v2] cpuidle: Fix the menu governor to boost IO
 performance

On Mon, 14 Sep 2009 20:54:08 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Tue, 15 Sep 2009 05:42:59 +0200 Arjan van de Ven
> <arjan@...radead.org> wrote:
> 
> > Rather than adding a new governor temporarily, this just puts the
> > fixes into the existing menu governor.
> 
> Oh, surprised.  I wasn't actually expecting that to happen.
> 
> <actually reads his email>
> 
> > I don't mind either way, will replace. 
> 
> OK.  I'm not particularly strongly opinionated either way.
> 
> The timing is awkward.  We could let it sit in Len's tree and
> linux-next for a couple of months or we could say what-the-hell and
> merge it.

If the performance impact wasn't this huge I'd say "let it sit".
As it is now, with a nearly 2x performance delta, I'd not be very happy
to expose linux users to this regression-like performance drop for
another 3 months. 

(especially given all the scheduler performance attention there is right
now; picking the wrong C state has clearly very high impact in similar
areas)

> 
> If the latter, your original merge plan sound better ;) But we should
> arrange for the new code to default to "on" for test coverage
> reasons. perhaps the original patch did that already?

the original patch defaulted to the new code yes.

redoing the split is not hard again.. just need to do a "cp" and put
the makefile glue back. I do like how the current patch shows exactly
which few things in the algorithm are changed..
(although it says 230 lines added, a lot of that are comments, the rest
isn't very big at all)



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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