linux-kernel - Re: [RFCv5 PATCH 35/46] sched: Disable energy-unfriendly nohz kicks

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Message-ID: <20150815093332.GC10304@worktop.programming.kicks-ass.net>
Date:	Sat, 15 Aug 2015 11:33:32 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Morten Rasmussen <morten.rasmussen@....com>
Cc:	mingo@...hat.com, vincent.guittot@...aro.org,
	daniel.lezcano@...aro.org,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	yuyang.du@...el.com, mturquette@...libre.com, rjw@...ysocki.net,
	Juri Lelli <Juri.Lelli@....com>, sgurrappadi@...dia.com,
	pang.xunlei@....com.cn, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [RFCv5 PATCH 35/46] sched: Disable energy-unfriendly nohz kicks

On Tue, Jul 07, 2015 at 07:24:18PM +0100, Morten Rasmussen wrote:
> With energy-aware scheduling enabled nohz_kick_needed() generates many
> nohz idle-balance kicks which lead to nothing when multiple tasks get
> packed on a single cpu to save energy. This causes unnecessary wake-ups
> and hence wastes energy. Make these conditions depend on !energy_aware()
> for now until the energy-aware nohz story gets sorted out.

The patch does slightly more; it also allows the kick if over utilized.

But disabling this will allow getting 'stuck' in certain over loaded
situations because we're not kicking the balancer.

I think you need more justification for doing this.

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