block: skip q->rq_qos check in rq_qos_done_bio()

If a bio has BIO_QOS_THROTTLED or BIO_QOS_MERGED set,
it implicitly guarantees that q->rq_qos is present.
Avoid re-checking q->rq_qos in this case and call
__rq_qos_done_bio() directly as a minor optimization.

Suggested-by : Yu Kuai <yukuai1@huaweicloud.com>

Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20250814082612.500845-2-nilay@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: shroffni

block/blk-rq-qos.h

@@ -142,8 +142,14 @@ static inline void rq_qos_done_bio(struct bio *bio)
 	    bio->bi_bdev && (bio_flagged(bio, BIO_QOS_THROTTLED) ||
 			     bio_flagged(bio, BIO_QOS_MERGED))) {
 		struct request_queue *q = bdev_get_queue(bio->bi_bdev);
-		if (q->rq_qos)
-			__rq_qos_done_bio(q->rq_qos, bio);
+
+		/*
+		 * If a bio has BIO_QOS_xxx set, it implicitly implies that
+		 * q->rq_qos is present. So, we skip re-checking q->rq_qos
+		 * here as an extra optimization and directly call
+		 * __rq_qos_done_bio().
+		 */
+		__rq_qos_done_bio(q->rq_qos, bio);
 	}
 }