blk-mq: use plug for devices that implement ->commits_rqs()

fix #28871358

commit b2c5d16b72df1116f05c9be16a630ac939d34101 upstream

If we have that hook, we know the driver handles bd->last == true in
a smart fashion. If it does, even for multiple hardware queues, it's
a good idea to flush batches of requests to the device, if we have
batches of requests from the submitter.
Reviewed-by: NMing Lei <ming.lei@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NBaolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: NJoseph Qi <joseph.qi@linux.alibaba.com>

block/blk-mq.c

@@ -1934,7 +1934,11 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 		/* bypass scheduler for flush rq */
 		blk_insert_flush(rq);
 		blk_mq_run_hw_queue(data.hctx, true);
-	} else if (plug && q->nr_hw_queues == 1) {
+	} else if (plug && (q->nr_hw_queues == 1 || q->mq_ops->commit_rqs)) {
+		/*
+		 * Use plugging if we have a ->commit_rqs() hook as well, as
+		 * we know the driver uses bd->last in a smart fashion.
+		 */
 		struct request *last = NULL;
 
 		blk_mq_put_ctx(data.ctx);