[PATCH 1/2] block: Optimize blk_mq_submit_bio() for the cache hit scenario

[Bart Van Assche <bvanassche@acm.org>]

Help the CPU branch predictor in case of a cache hit by handling the cache
hit scenario first.

Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 block/blk-mq.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7ee21346a41e..8d2aab4d9ba9 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3102,12 +3102,12 @@ void blk_mq_submit_bio(struct bio *bio)
 		goto queue_exit;
 
 new_request:
-	if (!rq) {
+	if (rq) {
+		blk_mq_use_cached_rq(rq, plug, bio);
+	} else {
 		rq = blk_mq_get_new_requests(q, plug, bio, nr_segs);
 		if (unlikely(!rq))
 			goto queue_exit;
-	} else {
-		blk_mq_use_cached_rq(rq, plug, bio);
 	}
 
 	trace_block_getrq(bio);