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SubjectRe: [PATCH 05/10] block: remove per-queue plugging
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On Tue, 2011-04-12 at 19:23 -0700, Linus Torvalds wrote:
> kernel/sched.c | 20 ++++++++++----------
> 1 files changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 48013633d792..a187c3fe027b 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -4111,20 +4111,20 @@ need_resched:
> try_to_wake_up_local(to_wakeup);
> }
> deactivate_task(rq, prev, DEQUEUE_SLEEP);
> +
> + /*
> + * If we are going to sleep and we have plugged IO queued, make
> + * sure to submit it to avoid deadlocks.
> + */
> + if (blk_needs_flush_plug(prev)) {
> + raw_spin_unlock(&rq->lock);
> + blk_flush_plug(prev);
> + raw_spin_lock(&rq->lock);
> + }
> }
> switch_count = &prev->nvcsw;
> }
>
> - /*
> - * If we are going to sleep and we have plugged IO queued, make
> - * sure to submit it to avoid deadlocks.
> - */
> - if (prev->state != TASK_RUNNING && blk_needs_flush_plug(prev)) {
> - raw_spin_unlock(&rq->lock);
> - blk_flush_plug(prev);
> - raw_spin_lock(&rq->lock);
> - }
> -
> pre_schedule(rq, prev);
>
> if (unlikely(!rq->nr_running))

Right, that cures the preemption problem. The reason I suggested placing
it where it was is that I'd like to keep all things that release
rq->lock in the middle of schedule() in one place, but I guess we can
cure that with some extra comments.





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