Commit 0c5bcc92 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Jens Axboe
Browse files

blk-mq: simplify the plug handling in blk_mq_submit_bio 



blk_mq_submit_bio has two different plug cases, one that uses full
plugging and a limited plugging one.

The limited plugging case is only used for a corner case that does
not matter in real life:

 - no ->commit_rqs (so not NVMe)
 - no shared tags (so not SCSI)
 - not rotational (so no old disk or floppy driver)
 - must have multiple queues (so no eMMC)

Remove the limited merging case and all the related junk to simplify
blk_mq_submit_bio and the functions called from it.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20211123160443.1315598-2-hch@lst.de


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent a4561f9f

block/blk-merge.c

+1 −8
Original line number Diff line number Diff line
@@ -1067,7 +1067,6 @@ static enum bio_merge_status blk_attempt_bio_merge(struct request_queue *q, 
 * @q: request_queue new bio is being queued at

 * @bio: new bio being queued

 * @nr_segs: number of segments in @bio

 * @same_queue_rq: output value, will be true if there's an existing request

 * from the passed in @q already in the plug list

 *

 * Determine whether @bio being queued on @q can be merged with the previous
@@ -1084,7 +1083,7 @@ static enum bio_merge_status blk_attempt_bio_merge(struct request_queue *q, 
 * Caller must ensure !blk_queue_nomerges(q) beforehand.

 */

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

		unsigned int nr_segs, bool *same_queue_rq)

		unsigned int nr_segs)

{

	struct blk_plug *plug;

	struct request *rq;
@@ -1096,12 +1095,6 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio, 
	/* check the previously added entry for a quick merge attempt */

	rq = rq_list_peek(&plug->mq_list);

	if (rq->q == q) {

		/*

		 * Only blk-mq multiple hardware queues case checks the rq in

		 * the same queue, there should be only one such rq in a queue

		 */

		*same_queue_rq = true;



		if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) ==

				BIO_MERGE_OK)

			return true;

block/blk-mq.c

+13 −55
Original line number Diff line number Diff line
@@ -2690,11 +2690,10 @@ static inline unsigned short blk_plug_max_rq_count(struct blk_plug *plug) 
}



static bool blk_mq_attempt_bio_merge(struct request_queue *q,

				     struct bio *bio, unsigned int nr_segs,

				     bool *same_queue_rq)

				     struct bio *bio, unsigned int nr_segs)

{

	if (!blk_queue_nomerges(q) && bio_mergeable(bio)) {

		if (blk_attempt_plug_merge(q, bio, nr_segs, same_queue_rq))

		if (blk_attempt_plug_merge(q, bio, nr_segs))

			return true;

		if (blk_mq_sched_bio_merge(q, bio, nr_segs))

			return true;
@@ -2705,8 +2704,7 @@ static bool blk_mq_attempt_bio_merge(struct request_queue *q, 
static struct request *blk_mq_get_new_requests(struct request_queue *q,

					       struct blk_plug *plug,

					       struct bio *bio,

					       unsigned int nsegs,

					       bool *same_queue_rq)

					       unsigned int nsegs)

{

	struct blk_mq_alloc_data data = {

		.q		= q,
@@ -2715,7 +2713,7 @@ static struct request *blk_mq_get_new_requests(struct request_queue *q, 
	};

	struct request *rq;



	if (blk_mq_attempt_bio_merge(q, bio, nsegs, same_queue_rq))

	if (blk_mq_attempt_bio_merge(q, bio, nsegs))

		return NULL;



	rq_qos_throttle(q, bio);
@@ -2751,8 +2749,7 @@ static inline bool blk_mq_can_use_cached_rq(struct request *rq, struct bio *bio) 
static inline struct request *blk_mq_get_request(struct request_queue *q,

						 struct blk_plug *plug,

						 struct bio *bio,

						 unsigned int nsegs,

						 bool *same_queue_rq)

						 unsigned int nsegs)

{

	struct request *rq;

	bool checked = false;
@@ -2762,8 +2759,7 @@ static inline struct request *blk_mq_get_request(struct request_queue *q, 
		if (rq && rq->q == q) {

			if (unlikely(!submit_bio_checks(bio)))

				return NULL;

			if (blk_mq_attempt_bio_merge(q, bio, nsegs,

						same_queue_rq))

			if (blk_mq_attempt_bio_merge(q, bio, nsegs))

				return NULL;

			checked = true;

			if (!blk_mq_can_use_cached_rq(rq, bio))
@@ -2781,7 +2777,7 @@ static inline struct request *blk_mq_get_request(struct request_queue *q, 
		return NULL;

	if (unlikely(!checked && !submit_bio_checks(bio)))

		goto out_put;

	rq = blk_mq_get_new_requests(q, plug, bio, nsegs, same_queue_rq);

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

	if (rq)

		return rq;

out_put:
@@ -2808,7 +2804,6 @@ void blk_mq_submit_bio(struct bio *bio) 
	const int is_sync = op_is_sync(bio->bi_opf);

	struct request *rq;

	struct blk_plug *plug;

	bool same_queue_rq = false;

	unsigned int nr_segs = 1;

	blk_status_t ret;
@@ -2823,7 +2818,7 @@ void blk_mq_submit_bio(struct bio *bio) 
		return;



	plug = blk_mq_plug(q, bio);

	rq = blk_mq_get_request(q, plug, bio, nr_segs, &same_queue_rq);

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

	if (unlikely(!rq))

		return;
@@ -2846,16 +2841,7 @@ void blk_mq_submit_bio(struct bio *bio) 
		return;

	}



	if (plug && (q->nr_hw_queues == 1 ||

	    blk_mq_is_shared_tags(rq->mq_hctx->flags) ||

	    q->mq_ops->commit_rqs || !blk_queue_nonrot(q))) {

		/*

		 * Use plugging if we have a ->commit_rqs() hook as well, as

		 * we know the driver uses bd->last in a smart fashion.

		 *

		 * Use normal plugging if this disk is slow HDD, as sequential

		 * IO may benefit a lot from plug merging.

		 */

	if (plug) {

		unsigned int request_count = plug->rq_count;

		struct request *last = NULL;
@@ -2873,40 +2859,12 @@ void blk_mq_submit_bio(struct bio *bio) 
		}



		blk_add_rq_to_plug(plug, rq);

	} else if (rq->rq_flags & RQF_ELV) {

		/* Insert the request at the IO scheduler queue */

	} else if ((rq->rq_flags & RQF_ELV) ||

		   (rq->mq_hctx->dispatch_busy &&

		    (q->nr_hw_queues == 1 || !is_sync))) {

		blk_mq_sched_insert_request(rq, false, true, true);

	} else if (plug && !blk_queue_nomerges(q)) {

		struct request *next_rq = NULL;



		/*

		 * We do limited plugging. If the bio can be merged, do that.

		 * Otherwise the existing request in the plug list will be

		 * issued. So the plug list will have one request at most

		 * The plug list might get flushed before this. If that happens,

		 * the plug list is empty, and same_queue_rq is invalid.

		 */

		if (same_queue_rq) {

			next_rq = rq_list_pop(&plug->mq_list);

			plug->rq_count--;

		}

		blk_add_rq_to_plug(plug, rq);

		trace_block_plug(q);



		if (next_rq) {

			trace_block_unplug(q, 1, true);

			blk_mq_try_issue_directly(next_rq->mq_hctx, next_rq);

		}

	} else if ((q->nr_hw_queues > 1 && is_sync) ||

		   !rq->mq_hctx->dispatch_busy) {

		/*

		 * There is no scheduler and we can try to send directly

		 * to the hardware.

		 */

		blk_mq_try_issue_directly(rq->mq_hctx, rq);

	} else {

		/* Default case. */

		blk_mq_sched_insert_request(rq, false, true, true);

		blk_mq_try_issue_directly(rq->mq_hctx, rq);

	}

}

block/blk.h

+1 −1
Original line number Diff line number Diff line
@@ -253,7 +253,7 @@ void blk_add_timer(struct request *req); 
const char *blk_status_to_str(blk_status_t status);



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

		unsigned int nr_segs, bool *same_queue_rq);

		unsigned int nr_segs);

bool blk_bio_list_merge(struct request_queue *q, struct list_head *list,

			struct bio *bio, unsigned int nr_segs);