linux-kernel - Re: [PATCH RESEND v9 10/10] sched: move cfs task on a CPU with higher capacity

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Message-ID: <20150220162641.GS5029@twins.programming.kicks-ass.net>
Date:	Fri, 20 Feb 2015 17:26:41 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Mike Galbraith <efault@....de>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>
Subject: Re: [PATCH RESEND v9 10/10] sched: move cfs task on a CPU with
 higher capacity

On Fri, Feb 20, 2015 at 02:54:09PM +0100, Vincent Guittot wrote:

> >>       if (rq->nr_running >= 2)
> >> +             return true;
> >
> > So this,

> >> +     sd = rcu_dereference(rq->sd);
> >> +     if (sd) {
> >> +             if ((rq->cfs.h_nr_running >= 1) &&
> >> +                             check_cpu_capacity(rq, sd)) {
> >> +                     kick = true;
> >> +                     goto unlock;
> >> +             }
> >> +     }
> >
> > vs this: how would we ever get here?
> >
> > If h_nr_running > 1, must then not nr_running > 1 as well?
> 
> you're right,
> but the test above can trig a kick with h_nr_running == 1 whereas the
> other tests may not

Duh, clearly I cannot read today.
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