linux-kernel - Re: [patch] CFS scheduler, -v19

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Date:	Fri, 13 Jul 2007 17:19:05 -0400
From:	Bill Davidsen <davidsen@....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>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: [patch] CFS scheduler, -v19

Ingo Molnar wrote:
> * Bill Davidsen <davidsen@....com> wrote:
> 
>>> I've taken mainline git tree (freshly integrated CFS!) out for a 
>>> multimedia spin.  I tested watching movies and listenign to music in 
>>> the presence of various sleep/burn loads, pure burn loads, and mixed 
>>> loads. All was peachy here.. I saw no frame drops or sound skips or 
>>> other artifacts under any load where the processor could possibly 
>>> meet demand.
>> I would agree with preliminary testing, save that if you get a lot of 
>> processes updating the screen at once, there seems to be a notable 
>> case of processes getting no CPU for 100-300ms, followed by a lot of 
>> CPU.
>>
>> I see this clearly with the "glitch1" test with four scrolling xterms 
>> and glxgears, but also watching videos with little busy processes on 
>> the screen. The only version where I never see this in test or with 
>> real use is cfs-v13.
> 
> just as a test, does this go away if you:
> 
> 	renice -20 pidof `Xorg`
> 
> i.e. is this connected to the way X is scheduled?
> 
Doing this slows down the display rates, but doesn't significantly help 
the smoothness of the gears.

> Another thing to check would be whether it goes away if you set the 
> granularity to some really finegrained value:
> 
>     echo 0 > /proc/sys/kernel/sched_wakeup_granularity_ns
>     echo 500000 > /proc/sys/kernel/sched_granularity_ns
> 
> this really pushes things - but it tests the theory whether this is 
> related to granularity.
> 
I didn't test this with standard Xorg priority, I should go back and try 
that. But it didn't really make much difference. The gears and scrolling 
xterms ran slower with Xorg at -20 with any sched settings. I'll do that 
as soon as a build finishes and I can reboot.

I should really go back to 2.6.21.6, 2.6.22 has many bizarre behaviors 
with FC6. Automount starts taking 30% of CPU (unused at the moment), the 
sensors applet doesn't work, etc. I hope over the weekend I can get bug 
reports out on all this, but there are lots of non-critical oddities.
> 	Ingo


-- 
Bill Davidsen <davidsen@....com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot
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