Re: [PATCH] sched: Remove WAKEUP_PREEMPT feature check in entity_tick

[Yong Zhang]

On Fri, Jul 29, 2011 at 01:45:33PM +0200, Peter Zijlstra wrote:
> On Fri, 2011-07-29 at 16:46 +0800, Yong Zhang wrote:
> > Let's take UP for example, we have cpu-hug task A and threadirq B.
> > 
> >         n tick          --->            n+1 tick
> > set_tsk_need_resched(A);
> >                 B comes in and
> >                 wake up thread-B;
> > 
> > So for system on which we disable WAKEUP_PREEMPT,
> > if we don't have that check, thread-B will wait until n+1 tick comes
> > to get to run.
> > But if we have that check, thread-B will get to run after IRQ-B returns.
> 
> But that's exactly what wakeup preemption is about, waking tasks don't
> get to preempt running tasks. So no doing that preemption is exactly
> right for !WAKEUP_PREEMPT.
> 
> Anyway, I've queued the removal patch since that removes all
> confusion ;-)

Yup, that sounds good. Thanks Peter.

-Yong

-- 
Only stand for myself
--
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/