linux-kernel - Re: [patch v3] sched: fix select_idle

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Message-ID: <1339435331.31548.19.camel@twins>
Date:	Mon, 11 Jun 2012 19:22:11 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Mike Galbraith <efault@....de>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Paul Turner <pjt@...gle.com>,
	Arjan Van De Ven <arjan@...ux.intel.com>
Subject: Re: [patch v3] sched: fix select_idle_sibling() induced bouncing

On Mon, 2012-06-11 at 18:57 +0200, Mike Galbraith wrote:

> Traversing an entire package is not only expensive, it also leads to tasks
> bouncing all over a partially idle and possible quite large package.  Fix
> that up by assigning a 'buddy' CPU to try to motivate.  Each buddy may try
> to motivate that one other CPU, if it's busy, tough, it may then try it's
> SMT sibling, but that's all this optimization is allowed to cost.
> 
> Sibling cache buddies are cross-wired to prevent bouncing.
> 
> Signed-off-by: Mike Galbraith <efault@....de>

The patch could do with a little comment on how you achieve the
cross-wiring because staring at the code I go cross-eyed again ;-)

Anyway, I think I'll grab it since nobody seems to have any objections
and the numbers seem good.

PJT any progress on your load-tracking stuff? Arjan is interested in the
avg runtime estimation it has to make the whole wake an idle thing
conditional on.
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