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Commit da41a589 authored by Robert Elliott's avatar Robert Elliott Committed by Jens Axboe
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blk-mq: Micro-optimize blk_queue_nomerges() check 



In blk_mq_make_request(), do the blk_queue_nomerges() check
outside the call to blk_attempt_plug_merge() to eliminate
function call overhead when nomerges=2 (disabled)

Signed-off-by: default avatarRobert Elliott <elliott@hp.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent eba71768

block/blk-core.c

+4 −4
Original line number Diff line number Diff line
@@ -1471,6 +1471,8 @@ bool bio_attempt_front_merge(struct request_queue *q, struct request *req, 
 * added on the elevator at this point.  In addition, we don't have

 * reliable access to the elevator outside queue lock.  Only check basic

 * merging parameters without querying the elevator.

 *

 * Caller must ensure !blk_queue_nomerges(q) beforehand.

 */

bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,

			    unsigned int *request_count)
@@ -1480,9 +1482,6 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio, 
	bool ret = false;

	struct list_head *plug_list;



	if (blk_queue_nomerges(q))

		goto out;



	plug = current->plug;

	if (!plug)

		goto out;
@@ -1561,7 +1560,8 @@ void blk_queue_bio(struct request_queue *q, struct bio *bio) 
	 * Check if we can merge with the plugged list before grabbing

	 * any locks.

	 */

	if (blk_attempt_plug_merge(q, bio, &request_count))

	if (!blk_queue_nomerges(q) &&

	    blk_attempt_plug_merge(q, bio, &request_count))

		return;



	spin_lock_irq(q->queue_lock);

block/blk-mq.c

+2 −1
Original line number Diff line number Diff line
@@ -1087,7 +1087,8 @@ static void blk_mq_make_request(struct request_queue *q, struct bio *bio) 
		return;

	}



	if (use_plug && blk_attempt_plug_merge(q, bio, &request_count))

	if (use_plug && !blk_queue_nomerges(q) &&

	    blk_attempt_plug_merge(q, bio, &request_count))

		return;



	if (blk_mq_queue_enter(q)) {