linux-kernel - Re: CFS review

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Message-ID: <20070828195525.GB30537@elte.hu>
Date:	Tue, 28 Aug 2007 21:55:25 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Willy Tarreau <w@....eu>
Cc:	Xavier Bestel <xavier.bestel@...e.fr>, Al Boldi <a1426z@...ab.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <efault@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: CFS review


* Willy Tarreau <w@....eu> wrote:

> On Tue, Aug 28, 2007 at 10:02:18AM +0200, Ingo Molnar wrote:
> > 
> > * Xavier Bestel <xavier.bestel@...e.fr> wrote:
> > 
> > > Are you sure they are stalled ? What you may have is simple gears 
> > > running at a multiple of your screen refresh rate, so they only appear 
> > > stalled.
> > > 
> > > Plus, as said Linus, you're not really testing the kernel scheduler. 
> > > gears is really bad benchmark, it should die.
> > 
> > i like glxgears as long as it runs on _real_ 3D hardware, because there 
> > it has minimal interaction with X and so it's an excellent visual test 
> > about consistency of scheduling. You can immediately see (literally) 
> > scheduling hickups down to a millisecond range (!). In this sense, if 
> > done and interpreted carefully, glxgears gives more feedback than many 
> > audio tests. (audio latency problems are audible, but on most sound hw 
> > it takes quite a bit of latency to produce an xrun.) So basically 
> > glxgears is the "early warning system" that tells us about the potential 
> > for xruns earlier than an xrun would happen for real.
> > 
> > [ of course you can also run all the other tools to get numeric results,
> >   but glxgears is nice in that it gives immediate visual feedback. ]
> 
> Al could also test ocbench, which brings visual feedback without 
> harnessing the X server : http://linux.1wt.eu/sched/
> 
> I packaged it exactly for this problem and it has already helped. It 
> uses X after each loop, so if you run it with large run time, X is 
> nearly not sollicitated.

yeah, and ocbench is one of my favorite cross-task-fairness tests - i 
dont release a CFS patch without checking it with ocbench first :-)

	Ingo
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