linux-kernel - Re: CFS review

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Date:	Wed, 29 Aug 2007 09:11:10 -0400
From:	Bill Davidsen <davidsen@....com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Al Boldi <a1426z@...ab.com>, Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <efault@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: CFS review

Ingo Molnar wrote:
> * Bill Davidsen <davidsen@....com> wrote:
>
>   
>>> There is another way to show the problem visually under X 
>>> (vesa-driver), by starting 3 gears simultaneously, which after 
>>> laying them out side-by-side need some settling time before 
>>> smoothing out.  Without __update_curr it's absolutely smooth from 
>>> the start.
>>>       
>> I posted a LOT of stuff using the glitch1 script, and finally found a 
>> set of tuning values which make the test script run smooth. See back 
>> posts, I don't have them here.
>>     
>
> but you have real 3D hw and DRI enabled, correct? In that case X uses up 
> almost no CPU time and glxgears makes most of the processing. That is 
> quite different from the above software-rendering case, where X spends 
> most of the CPU time.
>   

No, my test machine for that is a compile server, and uses the built-in 
motherboard graphics which are very limited. This is not in any sense a 
graphics powerhouse, it is used to build custom kernels and 
applications, and for testing of kvm and xen, and I grabbed it because 
it had the only Core2 CPU I could reboot to try new kernel versions and 
"from cold boot" testing, discovered the graphics smoothness issue by 
having several windows open on compiles, and developed the glitch1 
script as a way to reproduce it.

The settings I used, features=14, granularity=500000, work to improve 
smoothness on other machines for other uses, but they do seem to impact 
performance for compiles, video processing, etc, so they are not optimal 
for general use. I regard the existence of these tuning knobs as one of 
the real strengths of CFS, when you change the tuning it has a visible 
effect.

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

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