linux-kernel - Re: [patch] CFS (Completely Fair Scheduler), v2

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Message-ID: <20070417061849.GA12385@elte.hu>
Date:	Tue, 17 Apr 2007 08:18:49 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Gene Heskett <gene.heskett@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Williams <pwil3058@...pond.net.au>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Willy Tarreau <w@....eu>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>
Subject: Re: [patch] CFS (Completely Fair Scheduler), v2


* Gene Heskett <gene.heskett@...il.com> wrote:

> This one (v2-rc2) is not a keeper I'm sorry to say, Ingo.  v2-rc0 was 
> much better.  Watching amanda run with htop, kmails composer is being 
> subjected to 5 to 10 second pauses, and htop says that gzip -best 
> isn't getting more that 15% of the cpu, and the /amandatapes drive is 
> being written to in a regular pattern that seems to be the cause of 
> the pauses according to gkrellm, which also seems to track the size of 
> the writes, and can show anything from 4.3k to 54 megs as being 
> written in one cycle of its screen update.

ok - fortunately the delta between -v2-rc0 and -v2-final is pretty 
small. One difference is the child-runs-first fix. To restore the 
parent-runs-first logic, do this: 

	echo 0 > /proc/sys/kernel/sched_child_runs_first

does this make any difference?

If not then pretty much the only other change was the nice level tweak i 
did. Could you try to grab a few snapshots of scheduling state via 
something like:

   while sleep 1; do cat /proc/sched_debug >> to-ingo.txt; done

(and tell me the PID of the kmail composer, to make sure i'm checking 
the right task's behavior.)

also, as a separate experiment, could you perhaps run this script as 
root:

   cd /proc; for N in [1-9]*; do renice -n 0 $N; done

this will move all tasks in the system to nice level 0 and should make 
any nice level handling logic in the scheduler irrelevant. Do you have X 
reniced perhaps?

Lots of system threads have negative or positive nice levels, so once 
you have executed this script, only a reboot will be a practical way to 
restore it to the previous settings.

	Ingo
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