Re: [PATCH 1/4] block: add mq_ops->queue_rqs hook

If we have a list of requests in our plug list, send it to the driver in
one go, if possible. The driver must set mq_ops->queue_rqs() to support
this, if not the usual one-by-one path is used.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 block/blk-mq.c         | 26 +++++++++++++++++++++++---
 include/linux/blk-mq.h |  8 ++++++++
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index e02e7017db03..f24394cb2004 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c

@@ -2512,6 +2512,7 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 {
 	struct blk_mq_hw_ctx *this_hctx;
 	struct blk_mq_ctx *this_ctx;
+	struct request *rq;
 	unsigned int depth;
 	LIST_HEAD(list);
 

@@ -2520,7 +2521,28 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 	plug->rq_count = 0;
 
 	if (!plug->multiple_queues && !plug->has_elevator && !from_schedule) {
+		struct request_queue *q;
+
+		rq = rq_list_peek(&plug->mq_list);
+		q = rq->q;