On Sun, 2017-05-28 at 18:50 +0800, Ming Lei wrote: > On Sat, May 27, 2017 at 09:49:27PM +0000, Bart Van Assche wrote: > > On Sat, 2017-05-27 at 22:21 +0800, Ming Lei wrote: > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > > > index 032045841856..84cce67caee3 100644 > > > --- a/block/blk-mq.c > > > +++ b/block/blk-mq.c > > > @@ -168,8 +168,6 @@ void blk_mq_quiesce_queue(struct request_queue *q) > > > unsigned int i; > > > bool rcu = false; > > > > > > - __blk_mq_stop_hw_queues(q, true); > > > - > > > spin_lock_irq(q->queue_lock); > > > queue_flag_set(QUEUE_FLAG_QUIESCED, q); > > > spin_unlock_irq(q->queue_lock); > > > @@ -198,7 +196,12 @@ void blk_mq_unquiesce_queue(struct request_queue *q) > > > queue_flag_clear(QUEUE_FLAG_QUIESCED, q); > > > spin_unlock_irq(q->queue_lock); > > > > > > - blk_mq_start_stopped_hw_queues(q, true); > > > + /* > > > + * During quiescing, requests can be inserted > > > + * to scheduler's queue or sw queue, so we run > > > + * queues for dispatching these requests. > > > + */ > > > + blk_mq_start_hw_queues(q); > > > } > > > EXPORT_SYMBOL_GPL(blk_mq_unquiesce_queue); > > > > This looks really weird to me. If blk_mq_quiesce_queue() doesn't stop any > > hardware queues, why should blk_mq_unquiesce_queue() start any hardware > > queues? > > Please see the above comment, especially in direct issue path, we have to > insert the request into sw/scheduler queue when queue is quiesced, > and these queued requests have to be dispatched out during unquiescing. > > I considered to sleep the current context under this situation, but > turns out it is more complicated to handle, given we have very limited > queue depth, just let applications consumes all, then wait. Hello Ming, The above seems to me to be an argument to *run* the queue from inside blk_mq_unquiesce_queue() instead of *starting* stopped queues from inside that function. Bart.
