linux-kernel - Re: [PATCH 3/3] sched: Disable affine wakeups by default

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Date:	Mon, 26 Oct 2009 05:38:27 +0100
From:	Mike Galbraith <efault@....de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Arjan van de Ven <arjan@...radead.org>, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] sched: Disable affine wakeups by default

On Mon, 2009-10-26 at 02:53 +0100, Peter Zijlstra wrote:
> On Sun, 2009-10-25 at 23:04 +0100, Mike Galbraith wrote:
> >                 if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
> > -                   cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
> > +                               (level == SD_LV_SIBLING || level == SD_LV_MC)) {
> 
> quick comment without actually having looked at the patch, we should
> really get rid of sd->level and encode properties of the sched domains
> in sd->flags.

Yeah, sounds right, while writing that, it looked kinda ugly.  I suppose
arch land needs to encode cache property somehow if I really want to be
able to target cache on multicore.  Booting becomes.. exciting when I
tinker down there.

While tinkering with this, I noticed that when mysql+oltp starts
tripping over itself, if you move to any momentarily idle cpu, it helps
get the load moving again, the tail improves.  Not hugely, but quite
measurable.  There seems to be benefit to be had throughout the load
spectrum, just gotta figure out how to retrieve it without losing
anything.

	-Mike

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