Commit 72e84e90 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Jens Axboe
Browse files

blk-mq: special case cached requests less 



Share the main merge / split / integrity preparation code between the
cached request vs newly allocated request cases, and add comments
explaining the cached request handling.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDamien Le Moal <dlemoal@kernel.org>
Tested-by: default avatarDamien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20240124092658.2258309-4-hch@lst.de


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 337e89fe

block/blk-mq.c

+22 −19
Original line number Diff line number Diff line
@@ -2967,29 +2967,24 @@ void blk_mq_submit_bio(struct bio *bio) 
	struct blk_plug *plug = blk_mq_plug(bio);

	const int is_sync = op_is_sync(bio->bi_opf);

	struct blk_mq_hw_ctx *hctx;

	struct request *rq = NULL;

	unsigned int nr_segs = 1;

	struct request *rq;

	blk_status_t ret;



	bio = blk_queue_bounce(bio, q);



	/*

	 * If the plug has a cached request for this queue, try use it.

	 *

	 * The cached request already holds a q_usage_counter reference and we

	 * don't have to acquire a new one if we use it.

	 */

	rq = blk_mq_peek_cached_request(plug, q, bio->bi_opf);

	if (rq) {

		if (unlikely(bio_may_exceed_limits(bio, &q->limits))) {

			bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);

			if (!bio)

				return;

		}

		if (!bio_integrity_prep(bio))

			return;

		if (blk_mq_attempt_bio_merge(q, bio, nr_segs))

	if (!rq) {

		if (unlikely(bio_queue_enter(bio)))

			return;

		blk_mq_use_cached_rq(rq, plug, bio);

		goto done;

	}



	if (unlikely(bio_queue_enter(bio)))

		return;

	if (unlikely(bio_may_exceed_limits(bio, &q->limits))) {

		bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);

		if (!bio)
@@ -3001,11 +2996,14 @@ void blk_mq_submit_bio(struct bio *bio) 
	if (blk_mq_attempt_bio_merge(q, bio, nr_segs))

		goto queue_exit;



	if (!rq) {

		rq = blk_mq_get_new_requests(q, plug, bio, nr_segs);

		if (unlikely(!rq))

			goto queue_exit;

	} else {

		blk_mq_use_cached_rq(rq, plug, bio);

	}



done:

	trace_block_getrq(bio);



	rq_qos_track(q, rq, bio);
@@ -3039,6 +3037,11 @@ void blk_mq_submit_bio(struct bio *bio) 
	return;



queue_exit:

	/*

	 * Don't drop the queue reference if we were trying to use a cached

	 * request and thus didn't acquire one.

	 */

	if (!rq)

		blk_queue_exit(q);

}