linux-kernel - Re: [PATCH v3 04/22] sched: don't need go to smaller sched domain

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Date:	Thu, 10 Jan 2013 04:16:46 +0100
From:	Mike Galbraith <efault@....de>
To:	Morten Rasmussen <Morten.Rasmussen@....com>
Cc:	Alex Shi <alex.shi@...el.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"bp@...en8.de" <bp@...en8.de>, "pjt@...gle.com" <pjt@...gle.com>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 04/22] sched: don't need go to smaller sched domain

On Wed, 2013-01-09 at 17:38 +0000, Morten Rasmussen wrote: 
> On Sat, Jan 05, 2013 at 08:37:33AM +0000, Alex Shi wrote:
> > If parent sched domain has no task allowed cpu find. neither find in
> > it's child. So, go out to save useless checking.
> > 
> > Signed-off-by: Alex Shi <alex.shi@...el.com>
> > ---
> >  kernel/sched/fair.c | 6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 3c7b09a..ecfbf8e 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3378,10 +3378,8 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
> >  			load_idx = sd->wake_idx;
> >  
> >  		group = find_idlest_group(sd, p, cpu, load_idx);
> 
> The previous patch changed the behavior of find_idlest_group() to
> returning the local group if it is suitable. This effectively means that
> you remove the recursive search for a suitable idle sched group. You
> could as well merge find_idlest_group() and find_idlest_cpu() to avoid
> iterating through the cpus of the same sched group twice.

find_idlest_* could stop when seeing 0 too, can't get much more idle.

-Mike

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