Re: [PATCH 4/4] sched: Idle task shortcut optimization

[Daniel Lezcano]

On 01/17/2014 04:23 PM, Peter Zijlstra wrote:
> On Fri, Jan 17, 2014 at 04:06:45PM +0100, Daniel Lezcano wrote:
> > > I suppose we could write something like:
> > >
> > > struct task_struct *pick_next_task(struct rq *rq, struct task_struct *prev)
> > > {
> > > 	const struct sched_class *class;
> > > 	struct task_struct *p;
> > >
> > > again:
> > > 	if (likely(rq->nr_running)) {
> > >
> > > 		if (likely(rq->nr_running == rq->cfs.h_nr_running))
> > > 			return fair_sched_class.pick_next_task(rq, prev);
> > >
> > > 		for_each_class(class) {
> > > 			p = class->pick_next_task(rq, prev);
> > > 			if (p)
> > > 				return p;
> > > 		}
> > > 	}
> > >
> > > 	if (idle_balance(rq))
> > > 		goto again;
> > >
> > > 	rq->idle_stamp = rq_clock(rq);
> > >
> > > 	return idle_sched_class.pick_next_task(rq, prev);
> > > }
> > >
> > > Which keeps idle_balance() before put_prev_task(), and by using
> > > idle_sched_clas.pick_next_task() doesn't rape the idle class interface
> > > like you did :-)
> >
> > But put_prev_task is called before pick_next_task, so idle_balance() is
> > called after now, no  ?
>
> No, put_prev_task() is called by the pick_next_task() that returns a
> task. So in the idle case above, the idle_sched_class.pick_next_task()
> will do the required put_prev_task().

Ah, ok. Let me try it.



--
 <http://www.linaro.org/> Linaro.org â Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/