blk-mq: pass hctx to blk_mq_dispatch_rq_list

All requests in the 'list' of blk_mq_dispatch_rq_list belong to same
hctx, so it is better to pass hctx instead of request queue, because
blk-mq's dispatch target is hctx instead of request queue.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Tested-by: Baolin Wang <baolin.wang7@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: Baolin Wang <baolin.wang7@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq-sched.c

@@ -96,10 +96,9 @@ static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 	struct elevator_queue *e = q->elevator;
 	LIST_HEAD(rq_list);
 	int ret = 0;
+	struct request *rq;
 
 	do {
-		struct request *rq;
-
 		if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
 			break;
 
@@ -131,7 +130,7 @@ static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 		 * in blk_mq_dispatch_rq_list().
 		 */
 		list_add(&rq->queuelist, &rq_list);
-	} while (blk_mq_dispatch_rq_list(q, &rq_list, true));
+	} while (blk_mq_dispatch_rq_list(rq->mq_hctx, &rq_list, true));
 
 	return ret;
 }
@@ -161,10 +160,9 @@ static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 	LIST_HEAD(rq_list);
 	struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
 	int ret = 0;
+	struct request *rq;
 
 	do {
-		struct request *rq;
-
 		if (!list_empty_careful(&hctx->dispatch)) {
 			ret = -EAGAIN;
 			break;
@@ -200,7 +198,7 @@ static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 		/* round robin for fair dispatch */
 		ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
 
-	} while (blk_mq_dispatch_rq_list(q, &rq_list, true));
+	} while (blk_mq_dispatch_rq_list(rq->mq_hctx, &rq_list, true));
 
 	WRITE_ONCE(hctx->dispatch_from, ctx);
 	return ret;
@@ -240,7 +238,7 @@ static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 	 */
 	if (!list_empty(&rq_list)) {
 		blk_mq_sched_mark_restart_hctx(hctx);
-		if (blk_mq_dispatch_rq_list(q, &rq_list, false)) {
+		if (blk_mq_dispatch_rq_list(hctx, &rq_list, false)) {
 			if (has_sched_dispatch)
 				ret = blk_mq_do_dispatch_sched(hctx);
 			else
@@ -253,7 +251,7 @@ static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 		ret = blk_mq_do_dispatch_ctx(hctx);
 	} else {
 		blk_mq_flush_busy_ctxs(hctx, &rq_list);
-		blk_mq_dispatch_rq_list(q, &rq_list, false);
+		blk_mq_dispatch_rq_list(hctx, &rq_list, false);
 	}
 
 	return ret;

block/blk-mq.c

@@ -1258,10 +1258,10 @@ static void blk_mq_handle_zone_resource(struct request *rq,
 /*
  * Returns true if we did some work AND can potentially do more.
  */
-bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
+bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 			     bool got_budget)
 {
-	struct blk_mq_hw_ctx *hctx;
+	struct request_queue *q = hctx->queue;
 	struct request *rq, *nxt;
 	bool no_tag = false;
 	int errors, queued;
@@ -1283,7 +1283,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
 
 		rq = list_first_entry(list, struct request, queuelist);
 
-		hctx = rq->mq_hctx;
+		WARN_ON_ONCE(hctx != rq->mq_hctx);
 		if (!got_budget && !blk_mq_get_dispatch_budget(q)) {
 			blk_mq_put_driver_tag(rq);
 			no_budget_avail = true;

block/blk-mq.h

@@ -40,7 +40,7 @@ struct blk_mq_ctx {
 void blk_mq_exit_queue(struct request_queue *q);
 int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr);
 void blk_mq_wake_waiters(struct request_queue *q);
-bool blk_mq_dispatch_rq_list(struct request_queue *, struct list_head *, bool);
+bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *, bool);
 void blk_mq_add_to_requeue_list(struct request *rq, bool at_head,
 				bool kick_requeue_list);
 void blk_mq_flush_busy_ctxs(struct blk_mq_hw_ctx *hctx, struct list_head *list);