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

[Peter Zijlstra <peterz@infradead.org>]

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.