[PATCHv3 1/3] block: skip q->rq_qos check in rq_qos_done_bio()

[Nilay Shroff <nilay@linux.ibm.com>]

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>
---
 block/blk-rq-qos.h | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/block/blk-rq-qos.h b/block/blk-rq-qos.h
index 39749f4066fb..28125fc49eff 100644
--- a/block/blk-rq-qos.h
+++ b/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);
 	}
 }
 
-- 
2.50.1