linux-kernel - Re: BFS vs. mainline scheduler benchmarks and measurements

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Date:	Thu, 10 Sep 2009 05:15:27 +0200
From:	Mike Galbraith <efault@....de>
To:	Nikos Chantziaras <realnc@...or.de>
Cc:	Ingo Molnar <mingo@...e.hu>, Jens Axboe <jens.axboe@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Con Kolivas <kernel@...ivas.org>, linux-kernel@...r.kernel.org
Subject: Re: BFS vs. mainline scheduler benchmarks and measurements

On Wed, 2009-09-09 at 23:12 +0300, Nikos Chantziaras wrote:

> With your version of latt.c, I get these results with 2.6-tip vs 
> 2.6.31-rc9-bfs:
> 
> 
> (mainline)
> Averages:
> ------------------------------
>          Max            50 usec
>          Avg            12 usec
>          Stdev           3 usec
> 
> 
> (BFS)
> Averages:
> ------------------------------
>          Max           474 usec
>          Avg            11 usec
>          Stdev          16 usec
> 
> 
> However, the interactivity problems still remain.  Does that mean it's 
> not a latency issue?

Could be a fairness issue.  If X+client needs more than it's fair share
of CPU, there's nothing to do but use nice levels.  I'm stuck with
unaccelerated X (nvidia card), so if I want a good DVD watching or
whatever eye-candy experience while my box does a lot of other work, I
either have to use SCHED_IDLE/nice for the background stuff, or renice
X.  That's the down side of a fair scheduler.

There is another variant of latency related interactivity issue for the
desktop though, too LOW latency.  If X and clients are switching too
fast, redraw can look nasty, sliced/diced.

	-Mike

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