[PATCH v2 2/5] block/mq-deadline: Only use zone locking if necessary

[Bart Van Assche <bvanassche@xxxxxxx>]

Measurements have shown that limiting the queue depth to one for zoned
writes has a significant negative performance impact on zoned UFS devices.
Hence this patch that disables zone locking from the mq-deadline scheduler
for storage controllers that support pipelining zoned writes. This patch is
based on the following assumptions:
- Applications submit write requests to sequential write required zones
  in order.
- It happens infrequently that zoned write requests are reordered by the
  block layer.
- The storage controller does not reorder write requests that have been
  submitted to the same hardware queue. This is the case for UFS: the
  UFSHCI specification requires that UFS controllers process requests in
  order per hardware queue.
- The I/O priority of all pipelined write requests is the same per zone.
- Either no I/O scheduler is used or an I/O scheduler is used that
  submits write requests per zone in LBA order.

Cc: Damien Le Moal <damien.lemoal@xxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
 block/blk-zoned.c   |  3 ++-
 block/mq-deadline.c | 14 +++++++++-----
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index 0f9f97cdddd9..59560d1657e3 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -504,7 +504,8 @@ static int blk_revalidate_zone_cb(struct blk_zone *zone, unsigned int idx,
 		break;
 	case BLK_ZONE_TYPE_SEQWRITE_REQ:
 	case BLK_ZONE_TYPE_SEQWRITE_PREF:
-		if (!args->seq_zones_wlock) {
+		if (!blk_queue_pipeline_zoned_writes(q) &&
+		    !args->seq_zones_wlock) {
 			args->seq_zones_wlock =
 				blk_alloc_zone_bitmap(q->node, args->nr_zones);
 			if (!args->seq_zones_wlock)
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 6aa5daf7ae32..0bed2bdeed89 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -353,7 +353,8 @@ deadline_fifo_request(struct deadline_data *dd, struct dd_per_prio *per_prio,
 		return NULL;
 
 	rq = rq_entry_fifo(per_prio->fifo_list[data_dir].next);
-	if (data_dir == DD_READ || !blk_queue_is_zoned(rq->q))
+	if (data_dir == DD_READ || !blk_queue_is_zoned(rq->q) ||
+	    blk_queue_pipeline_zoned_writes(rq->q))
 		return rq;
 
 	/*
@@ -398,7 +399,8 @@ deadline_next_request(struct deadline_data *dd, struct dd_per_prio *per_prio,
 	if (!rq)
 		return NULL;
 
-	if (data_dir == DD_READ || !blk_queue_is_zoned(rq->q))
+	if (data_dir == DD_READ || !blk_queue_is_zoned(rq->q) ||
+	    blk_queue_pipeline_zoned_writes(rq->q))
 		return rq;
 
 	/*
@@ -526,8 +528,9 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd,
 	}
 
 	/*
-	 * For a zoned block device, if we only have writes queued and none of
-	 * them can be dispatched, rq will be NULL.
+	 * For a zoned block device that requires write serialization, if we
+	 * only have writes queued and none of them can be dispatched, rq will
+	 * be NULL.
 	 */
 	if (!rq)
 		return NULL;
@@ -933,7 +936,8 @@ static void dd_finish_request(struct request *rq)
 
 	atomic_inc(&per_prio->stats.completed);
 
-	if (blk_queue_is_zoned(q)) {
+	if (blk_queue_is_zoned(rq->q) &&
+	    !blk_queue_pipeline_zoned_writes(q)) {
 		unsigned long flags;
 
 		spin_lock_irqsave(&dd->zone_lock, flags);