linux-kernel - Re: [PATCH v2] sched: Fast idling of CPU when system is partially loaded

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Message-ID: <20140623185006.GH13930@laptop.programming.kicks-ass.net>
Date:	Mon, 23 Jun 2014 20:50:06 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Jason Low <jason.low2@...com>,
	Davidlohr Bueson <davidlohr@...com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched: Fast idling of CPU when system is partially
 loaded

On Mon, Jun 23, 2014 at 09:40:45AM -0700, Tim Chen wrote:

> > @@ -5886,7 +5886,7 @@ static inline void update_sg_lb_stats(st
> >  
> >  		sgs->group_load += load;
> >  		sgs->sum_nr_running += rq->nr_running;
> > -		if (overload && rq->nr_running > 1)
> > +		if (rq->nr_running > 1)
> >  			*overload = true;
> >  #ifdef CONFIG_NUMA_BALANCING
> >  		sgs->nr_numa_running += rq->nr_numa_running;

> With this change, we'll be returning the overload indicator 
> that we don't use for non-root domains, which will be
> extra work in sg_lb_stats as it loops through each rq checking
> the nr_running to update the indicator.  I was hoping to avoid
> that if possible.

What extra work? We already load nr_running and overloaded is on-stack
and should be quite dirty already due to that.

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