linux-kernel - Re: [RFC PATCH] sched: select_idle

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Message-ID: <1389880335.5418.46.camel@marge.simpson.net>
Date:	Thu, 16 Jan 2014 14:52:15 +0100
From:	Mike Galbraith <efault@....de>
To:	Alex Shi <alex.shi@...aro.org>
Cc:	mingo@...hat.com, peterz@...radead.org, morten.rasmussen@....com,
	vincent.guittot@...aro.org, daniel.lezcano@...aro.org,
	wangyun@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] sched: select_idle_sibling macro optimize

On Thu, 2014-01-16 at 21:13 +0800, Alex Shi wrote: 
> Add Mike Galbraith.
> 
> Any one like to give some comments?
> 
> On 01/15/2014 10:23 PM, Alex Shi wrote:
> > If the sd domain just has one group, then we must be caught the
> > 	i == target later, and then goes to deeper level domain.
> > So just skip this domain checking to save some instructions.
> > 
> > Signed-off-by: Alex Shi <alex.shi@...aro.org>
> > ---
> >  kernel/sched/fair.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index c7395d9..3265fbc 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -4196,6 +4196,11 @@ static int select_idle_sibling(struct task_struct *p, int target)
> >  	sd = rcu_dereference(per_cpu(sd_llc, target));
> >  	for_each_lower_domain(sd) {
> >  		sg = sd->groups;
> > +
> > +		/* skip single group domain */
> > +		if (sg == sg->next)
> > +			continue;

When is that gonna happen?

-Mike


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