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

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Date:	Tue, 17 Apr 2007 12:12:55 -0400
From:	Gene Heskett <gene.heskett@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
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

On Tuesday 17 April 2007, Ingo Molnar wrote:
>* 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:
>
I'm running 21-rc7-CFS-v2-rc0.1 now.

>	echo 0 > /proc/sys/kernel/sched_child_runs_first

This is currently a 1.  Reset to 0 by the above.

>does this make any difference?

Hard to tell, not much running except fetchmail/procmail and this composer.

>
>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
The crf1.txt is with it=1, the cfr0.txt is with it zeroed.

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

And I let the crf0 version run longer as I was looking for the composer's pid, 
but htop (or I) can't see it.  Even a ps -e isn't seeing it!  But its 
running, I'm actively typing in it.  So you get 3 files, the third one called 
ps-e.txt, in private mail.  I thought it was called composer, I really did.

>
>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



-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
I have many CHARTS and DIAGRAMS..
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