linux-kernel - Re: CFS review

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Message-ID: <20070829045316.GA15064@elte.hu>
Date:	Wed, 29 Aug 2007 06:53:16 +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:

> I have narrowed it down a bit to add_wait_runtime.

the scheduler is a red herring here. Could you "strace -ttt -TTT" one of 
the glxgears instances (and send us the cfs-debug-info.sh output, with 
CONFIG_SCHED_DEBUG=y and CONFIG_SCHEDSTATS=y as requested before) so 
that we can have a closer look?

i reproduced something similar and there the stall is caused by 1+ 
second select() delays on the X client<->server socket. The scheduler 
stats agree with that:

 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.

	Ingo
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