linux-kernel - Re: [PATCH 14/16] sched: make __update_entity_runnable

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Message-ID: <1341420714.19870.8.camel@laptop>
Date:	Wed, 04 Jul 2012 18:51:54 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Paul Turner <pjt@...gle.com>
Cc:	linux-kernel@...r.kernel.org, Venki Pallipadi <venki@...gle.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Ben Segall <bsegall@...gle.com>, Ingo Molnar <mingo@...e.hu>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: Re: [PATCH 14/16] sched: make __update_entity_runnable_avg() fast

On Wed, 2012-06-27 at 19:24 -0700, Paul Turner wrote:
> +#define LOAD_AVG_MAX_N 516 /* number of full periods it takes to produce max */

y=sqrt(sqrt(sqrt(sqrt(sqrt(0.5)))))
l(1/1024)/l(y)
319.99999999999999998938
1024*y^320
.99999999999999998976

So after only 320 periods the contribution of the term is too small to
matter.

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