2 files changed, 82 insertions, 9 deletions

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 4c72073830f3..1c52e56a19b1 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -7,6 +7,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/blk-mq.h>
+#include <linux/list_sort.h>
 
 #include <trace/events/block.h>
 
@@ -80,6 +81,37 @@ void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
 	blk_mq_run_hw_queue(hctx, true);
 }
 
+static int sched_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
+{
+	struct request *rqa = container_of(a, struct request, queuelist);
+	struct request *rqb = container_of(b, struct request, queuelist);
+
+	return rqa->mq_hctx > rqb->mq_hctx;
+}
+
+static bool blk_mq_dispatch_hctx_list(struct list_head *rq_list)
+{
+	struct blk_mq_hw_ctx *hctx =
+		list_first_entry(rq_list, struct request, queuelist)->mq_hctx;
+	struct request *rq;
+	LIST_HEAD(hctx_list);
+	unsigned int count = 0;
+	bool ret;
+
+	list_for_each_entry(rq, rq_list, queuelist) {
+		if (rq->mq_hctx != hctx) {
+			list_cut_before(&hctx_list, rq_list, &rq->queuelist);
+			goto dispatch;
+		}
+		count++;
+	}
+	list_splice_tail_init(rq_list, &hctx_list);
+
+dispatch:
+	ret = blk_mq_dispatch_rq_list(hctx, &hctx_list, count);
+	return ret;
+}
+
 #define BLK_MQ_BUDGET_DELAY	3		/* ms units */
 
 /*
@@ -90,20 +122,29 @@ void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
  * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
  * be run again.  This is necessary to avoid starving flushes.
  */
-static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
+static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 {
 	struct request_queue *q = hctx->queue;
 	struct elevator_queue *e = q->elevator;
+	bool multi_hctxs = false, run_queue = false;
+	bool dispatched = false, busy = false;
+	unsigned int max_dispatch;
 	LIST_HEAD(rq_list);
-	int ret = 0;
-	struct request *rq;
+	int count = 0;
+
+	if (hctx->dispatch_busy)
+		max_dispatch = 1;
+	else
+		max_dispatch = hctx->queue->nr_requests;
 
 	do {
+		struct request *rq;
+
 		if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
 			break;
 
 		if (!list_empty_careful(&hctx->dispatch)) {
-			ret = -EAGAIN;
+			busy = true;
 			break;
 		}
 
@@ -120,7 +161,7 @@ static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 			 * no guarantee anyone will kick the queue.  Kick it
 			 * ourselves.
 			 */
-			blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
+			run_queue = true;
 			break;
 		}
 
@@ -129,8 +170,42 @@ static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 		 * if this rq won't be queued to driver via .queue_rq()
 		 * in blk_mq_dispatch_rq_list().
 		 */
-		list_add(&rq->queuelist, &rq_list);
-	} while (blk_mq_dispatch_rq_list(rq->mq_hctx, &rq_list, 1));
+		list_add_tail(&rq->queuelist, &rq_list);
+		if (rq->mq_hctx != hctx)
+			multi_hctxs = true;
+	} while (++count < max_dispatch);
+
+	if (!count) {
+		if (run_queue)
+			blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
+	} else if (multi_hctxs) {
+		/*
+		 * Requests from different hctx may be dequeued from some
+		 * schedulers, such as bfq and deadline.
+		 *
+		 * Sort the requests in the list according to their hctx,
+		 * dispatch batching requests from same hctx at a time.
+		 */
+		list_sort(NULL, &rq_list, sched_rq_cmp);
+		do {
+			dispatched |= blk_mq_dispatch_hctx_list(&rq_list);
+		} while (!list_empty(&rq_list));
+	} else {
+		dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, count);
+	}
+
+	if (busy)
+		return -EAGAIN;
+	return !!dispatched;
+}
+
+static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
+{
+	int ret;
+
+	do {
+		ret = __blk_mq_do_dispatch_sched(hctx);
+	} while (ret == 1);
 
 	return ret;
 }
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 1b701e166681..a8fac4ff6fef 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1319,8 +1319,6 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 	if (list_empty(list))
 		return false;
 
-	WARN_ON(!list_is_singular(list) && nr_budgets);
-
 	/*
 	 * Now process all the entries, sending them to the driver.
 	 */