linux-kernel - Re: [PATCH v5 3/7] sched: set initial value of runnable avg for new forked task

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Message-ID: <20130508111516.GA6803@dyad.programming.kicks-ass.net>
Date:	Wed, 8 May 2013 13:15:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alex Shi <alex.shi@...el.com>
Cc:	Paul Turner <pjt@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Namhyung Kim <namhyung@...nel.org>,
	Mike Galbraith <efault@....de>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Michael Wang <wangyun@...ux.vnet.ibm.com>
Subject: Re: [PATCH v5 3/7] sched: set initial value of runnable avg for new
 forked task

On Tue, May 07, 2013 at 11:24:52AM +0800, Alex Shi wrote:
> It will give new forked task 1 ms extra running time. That will bring
> incorrect info if the new forked goes to sleep a while.
> But this info should benefit to some benchmarks like aim7,
> pthread_cond_broadcast. So I am convinced. :)
> 
> What's your opinion of this, Peter?

We're going to get it wrong anyhow (lack of crystal ball instruction);
overestimating the load seems like the best deal wrt latency for new tasks.

The only other option we could try (not sure its even worth trying) would be
half load.
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