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Commit 99e22598 authored by Jens Axboe's avatar Jens Axboe
Browse files

block: drop queue lock before calling __blk_run_queue() for kblockd punt 



If we know we are going to punt to kblockd, we can drop the queue
lock before calling into __blk_run_queue() since it only does a
safe bit test and a workqueue call. Since kblockd needs to grab
this very lock as one of the first things it does, it's a good
optimization to drop the lock before waking kblockd.

Signed-off-by: default avatarJens Axboe <jaxboe@fusionio.com>
parent b4cb290e

block/blk-core.c

+25 −8
Original line number Diff line number Diff line
@@ -295,7 +295,8 @@ EXPORT_SYMBOL(blk_sync_queue); 
 *

 * Description:

 *    See @blk_run_queue. This variant must be called with the queue lock

 *    held and interrupts disabled.

 *    held and interrupts disabled. If force_kblockd is true, then it is

 *    safe to call this without holding the queue lock.

 *

 */

void __blk_run_queue(struct request_queue *q, bool force_kblockd)
@@ -2671,9 +2672,23 @@ static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b) 
 */

static void queue_unplugged(struct request_queue *q, unsigned int depth,

			    bool from_schedule)

	__releases(q->queue_lock)

{

	trace_block_unplug(q, depth, !from_schedule);

	__blk_run_queue(q, from_schedule);



	/*

	 * If we are punting this to kblockd, then we can safely drop

	 * the queue_lock before waking kblockd (which needs to take

	 * this lock).

	 */

	if (from_schedule) {

		spin_unlock(q->queue_lock);

		__blk_run_queue(q, true);

	} else {

		__blk_run_queue(q, false);

		spin_unlock(q->queue_lock);

	}



}



static void flush_plug_callbacks(struct blk_plug *plug)
@@ -2729,10 +2744,11 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule) 
		BUG_ON(!(rq->cmd_flags & REQ_ON_PLUG));

		BUG_ON(!rq->q);

		if (rq->q != q) {

			if (q) {

			/*

			 * This drops the queue lock

			 */

			if (q)

				queue_unplugged(q, depth, from_schedule);

				spin_unlock(q->queue_lock);

			}

			q = rq->q;

			depth = 0;

			spin_lock(q->queue_lock);
@@ -2750,10 +2766,11 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule) 
		depth++;

	}



	if (q) {

	/*

	 * This drops the queue lock

	 */

	if (q)

		queue_unplugged(q, depth, from_schedule);

		spin_unlock(q->queue_lock);

	}



	local_irq_restore(flags);

}