[PATCH 06/11] block: optimize generic_make_request for direct to blk-mq issue

[Christoph Hellwig <hch@xxxxxx>]

Don't bother with the on-stack bio list if we know that we directly
issue to a request based driver that can't re-inject bios.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 block/blk-core.c | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 732d5b8d3cd25..e8c48203b2c55 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1008,6 +1008,18 @@ generic_make_request_checks(struct bio *bio)
 	return false;
 }
 
+static inline blk_qc_t __direct_make_request(struct bio *bio)
+{
+	struct request_queue *q = bio->bi_disk->queue;
+	blk_qc_t ret;
+
+	if (unlikely(bio_queue_enter(bio)))
+		return BLK_QC_T_NONE;
+	ret = blk_mq_make_request(q, bio);
+	blk_queue_exit(q);
+	return ret;
+}
+
 static blk_qc_t do_make_request(struct bio *bio,
 		struct bio_list bio_list_on_stack[2])
 {
@@ -1116,7 +1128,10 @@ blk_qc_t generic_make_request(struct bio *bio)
 		return BLK_QC_T_NONE;
 	}
 
-	return __generic_make_request(bio);
+	if (bio->bi_disk->queue->make_request_fn)
+		return __generic_make_request(bio);
+	return __direct_make_request(bio);
+
 }
 EXPORT_SYMBOL(generic_make_request);
 
@@ -1130,20 +1145,14 @@ EXPORT_SYMBOL(generic_make_request);
  */
 blk_qc_t direct_make_request(struct bio *bio)
 {
-	struct request_queue *q = bio->bi_disk->queue;
-	blk_qc_t ret;
-
-	if (WARN_ON_ONCE(q->make_request_fn)) {
+	if (WARN_ON_ONCE(bio->bi_disk->queue->make_request_fn)) {
 		bio_io_error(bio);
 		return BLK_QC_T_NONE;
 	}
+
 	if (!generic_make_request_checks(bio))
 		return BLK_QC_T_NONE;
-	if (unlikely(bio_queue_enter(bio)))
-		return BLK_QC_T_NONE;
-	ret = blk_mq_make_request(q, bio);
-	blk_queue_exit(q);
-	return ret;
+	return __direct_make_request(bio);
 }
 EXPORT_SYMBOL_GPL(direct_make_request);
 
-- 
2.26.1