linux-kernel - Re: CFS review

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Date:	Sun, 26 Aug 2007 19:27:07 +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:
> > > 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.)

Ok, I tried all your suggestions, but nothing works as smooth as removing 
__update_curr.

Does the problem show on your machine with the 3x gears under X-vesa test?


Thanks!

--
Al

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