@@ -637,6 +637,14 @@ static int hctx_active_show(void *data, struct seq_file *m)
 	return 0;
 }
 
+static int hctx_dispatch_busy_show(void *data, struct seq_file *m)
+{
+	struct blk_mq_hw_ctx *hctx = data;
+
+	seq_printf(m, "%u\n", hctx->dispatch_busy);
+	return 0;
+}
+
 static void *ctx_rq_list_start(struct seq_file *m, loff_t *pos)
 	__acquires(&ctx->lock)
 {

@@ -798,6 +806,7 @@ static const struct blk_mq_debugfs_attr blk_mq_debugfs_hctx_attrs[] = {
 	{"queued", 0600, hctx_queued_show, hctx_queued_write},
 	{"run", 0600, hctx_run_show, hctx_run_write},
 	{"active", 0400, hctx_active_show},
+	{"dispatch_busy", 0400, hctx_dispatch_busy_show},
 	{},
 };
 

@@ -219,15 +219,8 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 		}
 	} else if (has_sched_dispatch) {
 		blk_mq_do_dispatch_sched(hctx);
-	} else if (q->mq_ops->get_budget) {
-		/*
-		 * If we need to get budget before queuing request, we
-		 * dequeue request one by one from sw queue for avoiding
-		 * to mess up I/O merge when dispatch runs out of resource.
-		 *
-		 * TODO: get more budgets, and dequeue more requests in
-		 * one time.
-		 */
+	} else if (READ_ONCE(hctx->dispatch_busy)) {
+		/* dequeue request one by one from sw queue if queue is busy */
 		blk_mq_do_dispatch_ctx(hctx);
 	} else {
 		blk_mq_flush_busy_ctxs(hctx, &rq_list);

@@ -1073,6 +1073,31 @@ static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx **hctx,
 	return true;
 }
 
+/*
+ * Update dispatch busy with EWMA:
+ * - EWMA is one simple way to compute running average value
+ * - weight(7/8 and 1/8) is applied so that it can decrease exponentially
+ * - take 16 as current busy value for avoiding to get too small(0) result,
+ *   and this factor doesn't matter given EWMA decreases exponentially
+ */
+static void blk_mq_update_hctx_busy(struct blk_mq_hw_ctx *hctx, bool busy)
+{
+	const unsigned weight = 8;
+	unsigned int ewma;
+
+	if (hctx->queue->elevator)
+		return;
+
+	ewma = READ_ONCE(hctx->dispatch_busy);
+
+	ewma *= weight - 1;
+	if (busy)
+		ewma += 16;
+	ewma /= weight;
+
+	WRITE_ONCE(hctx->dispatch_busy, ewma);
+}
+
 #define BLK_MQ_RESOURCE_DELAY	3		/* ms units */
 
 /*

@@ -1209,8 +1234,11 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
 		else if (needs_restart && (ret == BLK_STS_RESOURCE))
 			blk_mq_delay_run_hw_queue(hctx, BLK_MQ_RESOURCE_DELAY);
 
+		blk_mq_update_hctx_busy(hctx, true);
+
 		return false;
-	}
+	} else
+		blk_mq_update_hctx_busy(hctx, false);
 
 	/*
 	 * If the host/device is unable to accept more work, inform the

@@ -35,9 +35,10 @@ struct blk_mq_hw_ctx {
 	struct sbitmap		ctx_map;
 
 	struct blk_mq_ctx	*dispatch_from;
+	unsigned int		dispatch_busy;
 
-	struct blk_mq_ctx	**ctxs;
 	unsigned int		nr_ctx;
+	struct blk_mq_ctx	**ctxs;
 
 	wait_queue_entry_t	dispatch_wait;
 	atomic_t		wait_index;