linux-kernel - Re: CFS review

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Message-ID: <20070829064303.GA32371@elte.hu>
Date:	Wed, 29 Aug 2007 08:43:03 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Al Boldi <a1426z@...ab.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <efault@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Keith Packard <keith.packard@...el.com>
Subject: Re: CFS review


* Al Boldi <a1426z@...ab.com> wrote:

> >  se.sleep_max             :          2194711437
> >  se.block_max             :                   0
> >  se.exec_max              :              977446
> >  se.wait_max              :             1912321
> >
> > the scheduler itself had a worst-case scheduling delay of 1.9
> > milliseconds for that glxgears instance (which is perfectly good - in
> > fact - excellent interactivity) - but the task had a maximum sleep time
> > of 2.19 seconds. So the 'glitch' was not caused by the scheduler.
> 
> 2.19sec is probably the time you need to lay them out side by side. 
> [...]

nope, i cleared the stats after i laid the glxgears out, via:

   for N in /proc/*/sched; do echo 0 > $N; done

and i did the strace (which showed a 1+ seconds latency) while the 
glxgears was not manipulated in any way.

> [...]  You see, gears sleeps when it is covered by another window, 
> [...]

none of the gear windows in my test were overlaid...

> [...] so once you lay them out it starts running, and that's when they 
> start to stutter for about 10sec.  After that they should run 
> smoothly, because they used up all the sleep bonus.

that's plain wrong - at least in the test i've reproduced. In any case, 
if that were the case then that would be visible in the stats. So please 
send me your cfs-debug-info.sh output captured while the test is running 
(with a CONFIG_SCHEDSTATS=y and CONFIG_SCHED_DEBUG=y kernel) - you can 
download it from:

   http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh

for best data, execute this before running it:

   for N in /proc/*/sched; do echo 0 > $N; done

> If you like, I can send you my straces, but they are kind of big 
> though, and you need to strace each gear, as stracing itself changes 
> the workload balance.

sure, send them along or upload them somewhere - but more importantly, 
please send the cfs-debug-info.sh output.

	Ingo
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