linux-kernel - Re: [patch] CFS scheduler, -v18

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Date:	Tue, 03 Jul 2007 09:12:23 +0200
From:	Mike Galbraith <efault@....de>
To:	Vegard Nossum <vegard.nossum@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [patch] CFS scheduler, -v18

On Mon, 2007-07-02 at 18:40 +0200, Vegard Nossum wrote:
> On 7/2/07, Ingo Molnar <mingo@...e.hu> wrote:
> > thx. As an initial matter, could you double-check whether your v18
> > kernel source has the patch below applied already?
> >
> >         Ingo
> >
> > Index: linux/kernel/sched_fair.c
> > ===================================================================
> > --- linux.orig/kernel/sched_fair.c
> > +++ linux/kernel/sched_fair.c
> > @@ -342,8 +342,9 @@ update_stats_enqueue(struct cfs_rq *cfs_
> >                 s64 tmp;
> >
> >                 if (se->wait_runtime < 0) {
> > -                       tmp = (0 - se->wait_runtime) << NICE_0_SHIFT;
> > -                       key += (tmp * se->load.inv_weight) >> WMULT_SHIFT;
> > +                       tmp = -se->wait_runtime;
> > +                       key += (tmp * se->load.inv_weight) >>
> > +                                       (WMULT_SHIFT - NICE_0_SHIFT);
> >                 } else {
> >                         tmp = se->wait_runtime * se->load.weight;
> >                         key -= tmp >> NICE_0_SHIFT;
> >
> >
> 
> It does.

Hi,

This doesn't appear to be a CFS problem.  I can reproduce the problem
easily in virgin 2.6.22-rc7 by starting xterm-spam at nice -1 or better.
As soon as xterm-spam can get enough CPU to keep the xterm fully busy,
it's game over, the xterm freezes.  The more accurate fairness of CFS to
sleepers just tips the balance quicker.  In mainline, the xterm has an
unfair advantage and maintains it indefinitely... until you tip the
scales just a wee bit, at which time it inverts.

	-Mike

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