Message-ID: <1427940712.2556.14.camel@j-VirtualBox>
Subject: Re: sched: Improve load balancing in the presence of idle CPUs
From: Jason Low <jason.low2@hp.com>
To: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: peterz@infradead.org, mingo@kernel.org,
        Daniel Lezcano <daniel.lezcano@linaro.org>, riel@redhat.com,
        vincent.guittot@linaro.org, srikar@linux.vnet.ibm.com, pjt@google.com,
        benh@kernel.crashing.org, efault@gmx.de, linux-kernel@vger.kernel.org,
        iamjoonsoo.kim@lge.com, svaidy@linux.vnet.ibm.com,
        tim.c.chen@linux.intel.com, morten.rasmussen@arm.com,
        jason.low2@hp.com
Date: Wed, 01 Apr 2015 19:11:52 -0700
In-Reply-To: <551A5CCE.70008@linux.vnet.ibm.com>
References: <1427741729.5694.24.camel@j-VirtualBox>
	 <551A5CCE.70008@linux.vnet.ibm.com>
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On Tue, 2015-03-31 at 14:07 +0530, Preeti U Murthy wrote:
> On 03/31/2015 12:25 AM, Jason Low wrote:

> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index fdae26e..ba8ec1a 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -7644,7 +7644,7 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
> >  		 * balancing owner will pick it up.
> >  		 */
> >  		if (need_resched())
> > -			break;
> > +			goto end;
> 
> Why is this hunk needed?

In terms of the change in the need_resched() case, if the current CPU
doesn't complete iterating all of the CPUs, then this will make it not
update nohz.next_balance. This is so we can continue the balancing with
the next balancing owner without too much delay.

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