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

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Date:	Thu, 12 Jul 2007 08:41:23 -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?
>
>   
Partial answer: -10 didn't help with v16, I'll try more boost ASAP, but 
power has been spotty in upstate NY, 20k+ customers with none and the 
rest of us subject to "load shedding" with zero warning, and the test 
machines have UPS but no generator, so I hesitate to use them while 
power is unstable.
> 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.
>   

Will do, you suggested dropping sched_granularity_ns to 1000000 earlier, 
and that didn't do it, but I didn't change the wakeup, and will test 
these values later today.

-- 
bill davidsen <davidsen@....com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979

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