linux-kernel - Re: [PATCH RFC/TEST] sched: make sync affine wakeups work

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Date:	Tue, 6 May 2014 13:56:44 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Preeti Murthy <preeti.lkml@...il.com>
Cc:	Rik van Riel <riel@...hat.com>, umgwanakikbuti@...il.com,
	LKML <linux-kernel@...r.kernel.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Ingo Molnar <mingo@...nel.org>, george.mccollister@...il.com,
	ktkhai@...allels.com, Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Subject: Re: [PATCH RFC/TEST] sched: make sync affine wakeups work

On Sun, May 04, 2014 at 05:14:59PM +0530, Preeti Murthy wrote:
> As far as my understanding goes, the logic in select_task_rq_fair()
> does wake_affine() or calls select_idle_sibling() only at those
> levels of sched domains where the flag SD_WAKE_AFFINE is set.
> This flag is not set at the numa domain and hence they will not be
> balancing across numa nodes. So I don't understand how
> *these functions* are affecting NUMA placements.

It _is_ set at NUMA domains, just not on those > RECLAIM_DISTANCE. That
means you typically need a non-fully connected system and then the top
numa tier will not get wake affine.

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