linux-kernel - Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq

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Message-ID: <1361521033.5817.95.camel@marge.simpson.net>
Date:	Fri, 22 Feb 2013 09:17:13 +0100
From:	Mike Galbraith <efault@....de>
To:	Michael Wang <wangyun@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Turner <pjt@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>, alex.shi@...el.com,
	Ram Pai <linuxram@...ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq_fair()

On Fri, 2013-02-22 at 14:42 +0800, Michael Wang wrote:

> So this is trying to take care the condition when curr_cpu(local) and
> prev_cpu(remote) are on different nodes, which in the old world,
> wake_affine() won't be invoked, correct?

It'll be called any time this_cpu and prev_cpu aren't one and the same.
It'd be pretty silly to asking whether to pull_here or leave_there when
here and there are identical.

> Hmm...I think this maybe a good additional checking before enter balance
> path, but I could not estimate the cost to record the relationship at
> this moment of time...

It'd be pretty cheap, but I'd hate adding any cycles to the fast path
unless those cycles have one hell of a good payoff, so the caching would
have to show most excellent cold hard numbers (talk crazy ideas walk;).

-Mike

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