Commit 1c2d2fff authored by Jens Axboe's avatar Jens Axboe
Browse files

block: wire-up support for passthrough plugging 



Add support for plugging in passthrough path. When plugging is enabled, the
requests are added to a plug instead of getting dispatched to the driver.
And when the plug is finished, the whole batch gets dispatched via
->queue_rqs which turns out to be more efficient. Otherwise dispatching
used to happen via ->queue_rq, one request at a time.

Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220511054750.20432-3-joshi.k@samsung.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent ee692a21

block/blk-mq.c

+39 −34
Original line number Diff line number Diff line
@@ -2340,6 +2340,40 @@ void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, 
	blk_mq_hctx_mark_pending(hctx, ctx);

}



/*

 * Allow 2x BLK_MAX_REQUEST_COUNT requests on plug queue for multiple

 * queues. This is important for md arrays to benefit from merging

 * requests.

 */

static inline unsigned short blk_plug_max_rq_count(struct blk_plug *plug)

{

	if (plug->multiple_queues)

		return BLK_MAX_REQUEST_COUNT * 2;

	return BLK_MAX_REQUEST_COUNT;

}



static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)

{

	struct request *last = rq_list_peek(&plug->mq_list);



	if (!plug->rq_count) {

		trace_block_plug(rq->q);

	} else if (plug->rq_count >= blk_plug_max_rq_count(plug) ||

		   (!blk_queue_nomerges(rq->q) &&

		    blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE)) {

		blk_mq_flush_plug_list(plug, false);

		trace_block_plug(rq->q);

	}



	if (!plug->multiple_queues && last && last->q != rq->q)

		plug->multiple_queues = true;

	if (!plug->has_elevator && (rq->rq_flags & RQF_ELV))

		plug->has_elevator = true;

	rq->rq_next = NULL;

	rq_list_add(&plug->mq_list, rq);

	plug->rq_count++;

}



/**

 * blk_mq_request_bypass_insert - Insert a request at dispatch list.

 * @rq: Pointer to request to be inserted.
@@ -2353,7 +2387,12 @@ void blk_mq_request_bypass_insert(struct request *rq, bool at_head, 
				  bool run_queue)

{

	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;

	struct blk_plug *plug = current->plug;



	if (plug) {

		blk_add_rq_to_plug(plug, rq);

		return;

	}

	spin_lock(&hctx->lock);

	if (at_head)

		list_add(&rq->queuelist, &hctx->dispatch);
@@ -2676,40 +2715,6 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx, 
		hctx->queue->mq_ops->commit_rqs(hctx);

}



/*

 * Allow 2x BLK_MAX_REQUEST_COUNT requests on plug queue for multiple

 * queues. This is important for md arrays to benefit from merging

 * requests.

 */

static inline unsigned short blk_plug_max_rq_count(struct blk_plug *plug)

{

	if (plug->multiple_queues)

		return BLK_MAX_REQUEST_COUNT * 2;

	return BLK_MAX_REQUEST_COUNT;

}



static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)

{

	struct request *last = rq_list_peek(&plug->mq_list);



	if (!plug->rq_count) {

		trace_block_plug(rq->q);

	} else if (plug->rq_count >= blk_plug_max_rq_count(plug) ||

		   (!blk_queue_nomerges(rq->q) &&

		    blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE)) {

		blk_mq_flush_plug_list(plug, false);

		trace_block_plug(rq->q);

	}



	if (!plug->multiple_queues && last && last->q != rq->q)

		plug->multiple_queues = true;

	if (!plug->has_elevator && (rq->rq_flags & RQF_ELV))

		plug->has_elevator = true;

	rq->rq_next = NULL;

	rq_list_add(&plug->mq_list, rq);

	plug->rq_count++;

}



static bool blk_mq_attempt_bio_merge(struct request_queue *q,

				     struct bio *bio, unsigned int nr_segs)

{