[PATCH 5/6] block: don't reorder requests in blk_add_rq_to_plug

[Christoph Hellwig]

Add requests to the tail of the list instead of the front so that they
are queued up in submission order.

Remove the re-reordering in blk_mq_dispatch_plug_list, virtio_queue_rqs
and nvme_queue_rqs now that the list is ordered as expected.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 block/blk-mq.c             | 4 ++--
 drivers/block/virtio_blk.c | 2 +-
 drivers/nvme/host/pci.c    | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index ff0b819e35fc..270cfd9fc6b0 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1392,7 +1392,7 @@ static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)
 	 */
 	if (!plug->has_elevator && (rq->rq_flags & RQF_SCHED_TAGS))
 		plug->has_elevator = true;
-	rq_list_add_head(&plug->mq_list, rq);
+	rq_list_add_tail(&plug->mq_list, rq);
 	plug->rq_count++;
 }
 
@@ -2844,7 +2844,7 @@ static void blk_mq_dispatch_plug_list(struct blk_plug *plug, bool from_sched)
 			rq_list_add_tail(&requeue_list, rq);
 			continue;
 		}
-		list_add(&rq->queuelist, &list);
+		list_add_tail(&rq->queuelist, &list);
 		depth++;
 	} while (!rq_list_empty(&plug->mq_list));
 
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index a19f24c19140..c0cdba71f436 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -514,7 +514,7 @@ static void virtio_queue_rqs(struct rq_list *rqlist)
 		vq = this_vq;
 
 		if (virtblk_prep_rq_batch(req))
-			rq_list_add_head(&submit_list, req); /* reverse order */
+			rq_list_add_tail(&submit_list, req);
 		else
 			rq_list_add_tail(&requeue_list, req);
 	}
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index c3a00a13946d..39ba1d0c287d 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -943,7 +943,7 @@ static void nvme_queue_rqs(struct rq_list *rqlist)
 		nvmeq = req->mq_hctx->driver_data;
 
 		if (nvme_prep_rq_batch(nvmeq, req))
-			rq_list_add_head(&submit_list, req); /* reverse order */
+			rq_list_add_tail(&submit_list, req);
 		else
 			rq_list_add_tail(&requeue_list, req);
 	}
-- 
2.45.2