[PATCH v4 10/11] block: mq-deadline: Handle requeued requests correctly

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

Start dispatching from the start of a zone instead of from the starting
position of the most recently dispatched request.

If a zoned write is requeued with an LBA that is lower than already
inserted zoned writes, make sure that it is submitted first.

Cc: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 block/mq-deadline.c | 34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index b482b707cb37..6c196182f86c 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -156,13 +156,28 @@ deadline_latter_request(struct request *rq)
 	return NULL;
 }
 
-/* Return the first request for which blk_rq_pos() >= pos. */
+/*
+ * Return the first request for which blk_rq_pos() >= @pos. For zoned devices,
+ * return the first request after the highest zone start <= @pos.
+ */
 static inline struct request *deadline_from_pos(struct dd_per_prio *per_prio,
 				enum dd_data_dir data_dir, sector_t pos)
 {
 	struct rb_node *node = per_prio->sort_list[data_dir].rb_node;
 	struct request *rq, *res = NULL;
 
+	if (!node)
+		return NULL;
+
+	rq = rb_entry_rq(node);
+	/*
+	 * A zoned write may have been requeued with a starting position that
+	 * is below that of the most recently dispatched request. Hence, for
+	 * zoned writes, start searching from the start of a zone.
+	 */
+	if (blk_rq_is_seq_zoned_write(rq))
+		pos -= round_down(pos, rq->q->limits.chunk_sectors);
+
 	while (node) {
 		rq = rb_entry_rq(node);
 		if (blk_rq_pos(rq) >= pos) {
@@ -812,6 +827,8 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
 		list_add(&rq->queuelist, &per_prio->dispatch);
 		rq->fifo_time = jiffies;
 	} else {
+		struct list_head *insert_before;
+
 		deadline_add_rq_rb(per_prio, rq);
 
 		if (rq_mergeable(rq)) {
@@ -824,7 +841,20 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
 		 * set expire time and add to fifo list
 		 */
 		rq->fifo_time = jiffies + dd->fifo_expire[data_dir];
-		list_add_tail(&rq->queuelist, &per_prio->fifo_list[data_dir]);
+		insert_before = &per_prio->fifo_list[data_dir];
+#ifdef CONFIG_BLK_DEV_ZONED
+		/*
+		 * Insert zoned writes such that requests are sorted by
+		 * position per zone.
+		 */
+		if (blk_rq_is_seq_zoned_write(rq)) {
+			struct request *rq2 = deadline_latter_request(rq);
+
+			if (rq2 && blk_rq_zone_no(rq2) == blk_rq_zone_no(rq))
+				insert_before = &rq2->queuelist;
+		}
+#endif
+		list_add_tail(&rq->queuelist, insert_before);
 	}
 }