linux-kernel - Re: CFS review

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Date:	Sun, 26 Aug 2007 01:15:26 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Al Boldi <a1426z@...ab.com>
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


* Al Boldi <a1426z@...ab.com> wrote:

> > ok. I think i might finally have found the bug causing this. Could 
> > you try the fix below, does your webserver thread-startup test work 
> > any better?
> 
> It seems to help somewhat, but the problem is still visible.  Even 
> v20.3 on 2.6.22.5 didn't help.
> 
> It does look related to ia-boosting, so I turned off __update_curr 
> like Roman mentioned, which had an enormous smoothing effect, but then 
> nice levels completely break down and lockup the system.

you can turn sleeper-fairness off via:

   echo 28 > /proc/sys/kernel/sched_features

another thing to try would be:

   echo 12 > /proc/sys/kernel/sched_features

(that's the new-task penalty turned off.)

Another thing to try would be to edit this:

        if (sysctl_sched_features & SCHED_FEAT_START_DEBIT)
                p->se.wait_runtime = -(sched_granularity(cfs_rq) / 2);

to:

        if (sysctl_sched_features & SCHED_FEAT_START_DEBIT)
                p->se.wait_runtime = -(sched_granularity(cfs_rq);

and could you also check 20.4 on 2.6.22.5 perhaps, or very latest -git? 
(Peter has experienced smaller spikes with that.)

	Ingo
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