On Tue, Aug 20, 2013 at 08:25:53PM +0200, Oleg Nesterov wrote:
> On 08/20, Peter Zijlstra wrote:
> >
> > On Tue, Aug 20, 2013 at 06:33:12PM +0200, Oleg Nesterov wrote:
> > > + if (unlikely(prev->in_iowait)) {
> > > + raw_spin_lock_irq(&rq->lock);
> > > + rq->nr_iowait--;
> > > + raw_spin_unlock_irq(&rq->lock);
> > > + }
> >
> > This seems like the wrong place, this is where you return from
> > schedule() running another task,
>
> Yes, but prev is current, and rq should be "correct" for
> rq->nr_iowait-- ?
Yes its the right rq, but the wrong time.
> This local var should be equal to its value when this task called
> context_switch() in the past.
>
> Like any other variable, like "rq = raw_rq()" in io_schedule().
>
> > not where the task you just send to
> > sleep wakes up.
>
> sure, but currently io_schedule() does the same.
No it doesn't. It only does the decrement when the task is woken back
up. Not right after it switches out.
> Btw. Whatever we do, can't we unify io_schedule/io_schedule_timeout?
I suppose we could, a timeout of MAX_SCHEDULE_TIMEOUT will act like a
regular schedule, but it gets all the overhead of doing
schedule_timeout(). So I don't think its a win.
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