blk-mq: move getting driver tag and budget into one helper

Move code for getting driver tag and budget into one helper, so
blk_mq_dispatch_rq_list gets a bit simplified, and easier to read.

Meantime move updating of 'no_tag' and 'no_budget_available' into
the branch for handling partial dispatch because that is exactly
consumer of the two local variables.

Also rename the parameter of 'got_budget' as 'ask_budget'.

No functional change.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Tested-by: Baolin Wang <baolin.wang7@gmail.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@infradead.org>
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.c

@@ -1255,18 +1255,50 @@ static void blk_mq_handle_zone_resource(struct request *rq,
 	__blk_mq_requeue_request(rq);
 }
 
+enum prep_dispatch {
+	PREP_DISPATCH_OK,
+	PREP_DISPATCH_NO_TAG,
+	PREP_DISPATCH_NO_BUDGET,
+};
+
+static enum prep_dispatch blk_mq_prep_dispatch_rq(struct request *rq,
+						  bool need_budget)
+{
+	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
+
+	if (need_budget && !blk_mq_get_dispatch_budget(rq->q)) {
+		blk_mq_put_driver_tag(rq);
+		return PREP_DISPATCH_NO_BUDGET;
+	}
+
+	if (!blk_mq_get_driver_tag(rq)) {
+		/*
+		 * The initial allocation attempt failed, so we need to
+		 * rerun the hardware queue when a tag is freed. The
+		 * waitqueue takes care of that. If the queue is run
+		 * before we add this entry back on the dispatch list,
+		 * we'll re-run it below.
+		 */
+		if (!blk_mq_mark_tag_wait(hctx, rq)) {
+			blk_mq_put_dispatch_budget(rq->q);
+			return PREP_DISPATCH_NO_TAG;
+		}
+	}
+
+	return PREP_DISPATCH_OK;
+}
+
 /*
  * Returns true if we did some work AND can potentially do more.
  */
 bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 			     bool got_budget)
 {
+	enum prep_dispatch prep;
 	struct request_queue *q = hctx->queue;
 	struct request *rq, *nxt;
-	bool no_tag = false;
 	int errors, queued;
 	blk_status_t ret = BLK_STS_OK;
-	bool no_budget_avail = false;
 	LIST_HEAD(zone_list);
 
 	if (list_empty(list))
@@ -1284,31 +1316,9 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 		rq = list_first_entry(list, struct request, queuelist);
 
 		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;
+		prep = blk_mq_prep_dispatch_rq(rq, !got_budget);
+		if (prep != PREP_DISPATCH_OK)
 			break;
-		}
-
-		if (!blk_mq_get_driver_tag(rq)) {
-			/*
-			 * The initial allocation attempt failed, so we need to
-			 * rerun the hardware queue when a tag is freed. The
-			 * waitqueue takes care of that. If the queue is run
-			 * before we add this entry back on the dispatch list,
-			 * we'll re-run it below.
-			 */
-			if (!blk_mq_mark_tag_wait(hctx, rq)) {
-				blk_mq_put_dispatch_budget(q);
-				/*
-				 * For non-shared tags, the RESTART check
-				 * will suffice.
-				 */
-				if (hctx->flags & BLK_MQ_F_TAG_SHARED)
-					no_tag = true;
-				break;
-			}
-		}
 
 		list_del_init(&rq->queuelist);
 
@@ -1361,6 +1371,10 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 	 */
 	if (!list_empty(list)) {
 		bool needs_restart;
+		/* For non-shared tags, the RESTART check will suffice */
+		bool no_tag = prep == PREP_DISPATCH_NO_TAG &&
+                        (hctx->flags & BLK_MQ_F_TAG_SHARED);
+		bool no_budget_avail = prep == PREP_DISPATCH_NO_BUDGET;
 
 		/*
 		 * If we didn't flush the entire list, we could have told