linux-kernel - Re: CFS review

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Date:	Tue, 28 Aug 2007 21:19:25 +0200
From:	Willy Tarreau <w@....eu>
To:	Ingo Molnar <mingo@...e.hu>
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

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. 

Willy

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