linux-kernel - Re: [patch] Re: scheduler oddity [bug?]

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Date:	Mon, 09 Mar 2009 14:27:47 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Mike Galbraith <efault@....de>
Cc:	Ingo Molnar <mingo@...e.hu>, Balazs Scheidler <bazsi@...abit.hu>,
	linux-kernel@...r.kernel.org, Willy Tarreau <w@....eu>
Subject: Re: [patch] Re: scheduler oddity [bug?]

On Mon, 2009-03-09 at 14:16 +0100, Mike Galbraith wrote:
> On Mon, 2009-03-09 at 12:04 +0100, Peter Zijlstra wrote:
> 
> > OK, talked a bit with Ingo, the reason you're doing is that avg_overlap
> > can easily grow stale.. I can see that happen indeed.
> > 
> > So the 'perfect' thing would be a task-runtime decay, barring that the
> > preemption thing seems a sane enough hart-beat of a task.
> > 
> > How does the below look to you?
> 
> Other than the fact that the test for sync reject is currently
> avg_overlap > sysctl_sched_migration_cost, looks fine to me.  Having it
> capped at the boundary is probably the better way to go.

Ah, yes, and looking at update_avg() we'll also discard the lower 3
bits, so we'll never actually reach.

So I guess it should read something like:

  update_avg(&prev->se.avg_overlap, 2*sysctl_sched_migration_cost);

or somesuch.

Does it actually solve the reported problem? I've only thought about the
issue so far :-)

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