linux-kernel - Re: [PATCH V2] sched: Improve load balancing in the presence of idle CPUs

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Message-ID: <20150330140131.GZ23123@twins.programming.kicks-ass.net>
Date:	Mon, 30 Mar 2015 16:01:31 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Morten Rasmussen <morten.rasmussen@....com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	"srikar@...ux.vnet.ibm.com" <srikar@...ux.vnet.ibm.com>,
	"pjt@...gle.com" <pjt@...gle.com>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	"efault@....de" <efault@....de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
	"svaidy@...ux.vnet.ibm.com" <svaidy@...ux.vnet.ibm.com>,
	"tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
	"jason.low2@...com" <jason.low2@...com>
Subject: Re: [PATCH V2] sched: Improve load balancing in the presence of idle
 CPUs

On Mon, Mar 30, 2015 at 03:29:09PM +0200, Vincent Guittot wrote:
> On 30 March 2015 at 14:24, Peter Zijlstra <peterz@...radead.org> wrote:
> > @@ -7647,6 +7648,8 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
> >                         break;
> >
> >                 rq = cpu_rq(balance_cpu);
> > +               if (rq == this_rq)
> > +                       done = true;
> 
> AFAICT, this can't happen because we start the for_each _cpu loop with:
> if (balance_cpu == this_cpu || !idle_cpu(balance_cpu))
> continue;

Oh hey, look at me being blind ;-)
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