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

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Message-Id: <1256536078.7117.67.camel@marge.simson.net>
Date:	Mon, 26 Oct 2009 06:47:58 +0100
From:	Mike Galbraith <efault@....de>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] sched: Disable affine wakeups by default

On Sun, 2009-10-25 at 22:36 -0700, Arjan van de Ven wrote:
> On Mon, 26 Oct 2009 06:08:54 +0100
> Mike Galbraith <efault@....de> wrote:

> > > 
> > > or we just use SD_WAKE_AFFINE / SD_BALANCE_WAKE for this...
> > 
> > I don't see how.  Oh, you mean another domain level, top level being
> > cache property, and turn off when degenerating?  That looks like it'd
> > be a problem, but adding SD_CACHE_SIBLING or whatnot should work.
> > Problem is how to gain knowledge of whether multicores share a cache
> > or not.
> 
> Actually I meant setting the SD_BALANCE_WAKE flag for the SMT and MC
> domains (and then making sure that "MC" really means "shares LLC" in
> the arch code), and then using this as indication in the sched code..

I don't think we can do that, because SD_WAKE_BALANCE already has a
different meaning.  SD_WAKE_AFFINE could be used though, affine wakeups
have always been a cache thing, and for trying to keep things affine to
a package or whatnot, we have SD_PREFER_LOCAL.  Sounds clean to me.

> if you're a multicore domain you better have a shared cache.. that's
> what it should mean. If it does not we should fix that.

Sounds reasonable to me.  I'll go make explosions.

	-Mike

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