linux-kernel - Re: [RFCv5 PATCH 30/46] sched: Add cpu capacity awareness to wakeup balancing

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Message-ID: <20150813182409.GB19282@twins.programming.kicks-ass.net>
Date:	Thu, 13 Aug 2015 20:24:09 +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 30/46] sched: Add cpu capacity awareness to wakeup
 balancing

On Tue, Jul 07, 2015 at 07:24:13PM +0100, Morten Rasmussen wrote:
> 
> This patch adds capacity awareness to find_idlest_{group,queue} (used by
> SD_BALANCE_{FORK,EXEC}) such that groups/cpus that can accommodate the
> waking task based on task utilization are preferred. In addition, wakeup
> of existing tasks (SD_BALANCE_WAKE) is sent through
> find_idlest_{group,queue} if the task doesn't fit the capacity of the
> previous cpu to allow it to escape (override wake_affine) when
> necessary instead of relying on periodic/idle/nohz_idle balance to
> eventually sort it out.
> 

That's policy not guided by the energy model.. Also we need something
clever for the wakeup balancing, the current stuff all stinks :/
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