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

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Date:	Tue, 19 Jun 2012 01:47:57 -0700
From:	Paul Turner <pjt@...gle.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Mike Galbraith <efault@....de>,
	lkml <linux-kernel@...r.kernel.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Arjan Van De Ven <arjan@...ux.intel.com>
Subject: Re: [patch v3] sched: fix select_idle_sibling() induced bouncing

On Mon, Jun 11, 2012 at 10:22 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 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.

I'm still pretty much completely clobbered with internal stuff :( but
it's on my agenda to put some cycles towards this week (and weekend).
I'll say by Monday/Tuesday with a hopefully by-Friday.

We've gotten a lot of of test hours on it internally so I'm
comfortable posting a non-RFC mergable series.

- Paul
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