linux-kernel - Re: [PATCH v2] sched: keep quiescent cpu out of idle balance loop

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Message-ID: <1392974126.5451.109.camel@marge.simpson.net>
Date:	Fri, 21 Feb 2014 10:15:26 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Lei Wen <adrian.wenl@...il.com>
Cc:	Lei Wen <leiwen@...vell.com>,
	Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
	preeti.lkml@...il.com, daniel.lezcano@...aro.org,
	viresh.kumar@...aro.org, xjian@...vell.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched: keep quiescent cpu out of idle balance loop

On Fri, 2014-02-21 at 09:34 +0100, Mike Galbraith wrote:

> I think the construction stuff works fine, and !->sd is the perfect cue
> to tell various things to keep their grubby mitts off of a CPU.

Take idle_balance() for instance.. not much point in dropping rq->lock
just to take it again after doing _nothing_, and we certainly wouldn't
want to go play load balancer for connected CPUs anyway, we might get
something much more important to do RSN.

(that applies to rt in general - go off and play load balancer in the
SCHED_OTHER slums?  Surely you jest, elite snobs don't do skut work,
they actually might get their hands dirty;)

Or, at user discretion, telling CPUPRI stuff that no load balancing also
means no rt balancing, i.e. the user assumes responsibility for ALL task
placement, so we don't need to call neutered functions or spend cycles
maintaining data we will have no use for until the user tells us he is
finished with these CPUs.

etc.

-Mike 

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