Re: sched: how to pick runqueue when checking task hot?

[Mike Galbraith <mgalbraith@suse.de>]

On Fri, 2014-06-06 at 12:15 +0200, Peter Zijlstra wrote:

> > --- a/kernel/sched/fair.c	Fri Jun  6 12:37:37 2014
> > +++ b/kernel/sched/fair.c	Fri Jun  6 14:32:34 2014
> > @@ -5051,7 +5051,7 @@ task_hot(struct task_struct *p, u64 now)
> >  	/*
> >  	 * Buddy candidates are cache hot:
> >  	 */
> > -	if (sched_feat(CACHE_HOT_BUDDY) && this_rq()->nr_running &&
> > +	if (sched_feat(CACHE_HOT_BUDDY) && task_rq(p)->nr_running &&
> >  			(&p->se == cfs_rq_of(&p->se)->next ||
> >  			 &p->se == cfs_rq_of(&p->se)->last))
> >  		return 1;
> 
> That does appear to make more sense indeed, seeing how buddies are pairs
> of tasks, so protecting a lone task doesn't make sense.
> 
> 
> Mike, how did you intend this code to work?

IIRC, this_rq()->nr_running was to say if we're idle, we don't care that
it's last/next, pull it.  Not sure I'm the one who did that, but could
be, I didn't look.

-Mike