On 08/20, Peter Zijlstra wrote:
>
> On Tue, Aug 20, 2013 at 06:33:12PM +0200, Oleg Nesterov wrote:
> > --- x/kernel/sched/core.c
> > +++ x/kernel/sched/core.c
> > @@ -2435,6 +2435,9 @@ need_resched:
> > rq->curr = next;
> > ++*switch_count;
> >
> > + if (unlikely(prev->in_iowait))
> > + rq->nr_iowait++;
> > +
> > context_switch(rq, prev, next); /* unlocks the rq */
> > /*
> > * The context switch have flipped the stack from under us
> > @@ -2442,6 +2445,12 @@ need_resched:
> > * this task called schedule() in the past. prev == current
> > * is still correct, but it can be moved to another cpu/rq.
> > */
> > + 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-- ?
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.
Btw. Whatever we do, can't we unify io_schedule/io_schedule_timeout?
Oleg.
--- x/kernel/sched/core.c
+++ x/kernel/sched/core.c
@@ -3939,16 +3939,7 @@ EXPORT_SYMBOL_GPL(yield_to);
*/
void __sched io_schedule(void)
{
- struct rq *rq = raw_rq();
-
- delayacct_blkio_start();
- atomic_inc(&rq->nr_iowait);
- blk_flush_plug(current);
- current->in_iowait = 1;
- schedule();
- current->in_iowait = 0;
- atomic_dec(&rq->nr_iowait);
- delayacct_blkio_end();
+ io_schedule_timeout(MAX_SCHEDULE_TIMEOUT);
}
EXPORT_SYMBOL(io_schedule);
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