linux-kernel - Re: CFS review

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Date:	Mon, 27 Aug 2007 07:06:41 +0300
From:	Al Boldi <a1426z@...ab.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	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:
> * Al Boldi <a1426z@...ab.com> wrote:
> > > and could you also check 20.4 on 2.6.22.5 perhaps, or very latest
> > > -git? (Peter has experienced smaller spikes with that.)
> >
> > Ok, I tried all your suggestions, but nothing works as smooth as
> > removing __update_curr.
>
> could you send the exact patch that shows what you did?

On 2.6.22.5-v20.3 (not v20.4):

340-    curr->delta_exec += delta_exec;
341-
342-    if (unlikely(curr->delta_exec > sysctl_sched_stat_granularity)) {
343://          __update_curr(cfs_rq, curr);
344-            curr->delta_exec = 0;
345-    }
346-    curr->exec_start = rq_of(cfs_rq)->clock;

> And could you
> also please describe it exactly which aspect of the workload you call
> 'smooth'. Could it be made quantitative somehow?

The 3x gears test shows the startup problem in a really noticeable way.  With 
v20.4 they startup surging and stalling periodically for about 10sec, then 
they are smooth.  With v20.3 + above patch they startup completely smooth.


Thanks!

--
Al
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