On Tue, Jul 11, 2017 at 08:18:51PM +0000, Bart Van Assche wrote:

On Wed, 2017-07-12 at 02:21 +0800, Ming Lei wrote:

quoted

Before mq IO scheduler is in, we always send the request to
dispatch list if .queue_rq() return busy. After mq IO scheduler
is introduced, we only do this way when scheduler is used in
case of direct issue. Actually we can do that when scheduler
isn't used too.

Signed-off-by: Ming Lei <redacted>
---
 block/blk-mq.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 041f7b7fa0d6..6e0fc80aa151 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c

@@ -1463,6 +1463,16 @@ static blk_qc_t request_to_qc_t(struct blk_mq_hw_ctx *hctx, struct request *rq)
 	return blk_tag_to_qc_t(rq->internal_tag, hctx->queue_num, true);
 }
 
+static void blk_mq_direct_dispatch(struct blk_mq_hw_ctx *hctx,
+				   struct request *rq)
+{
+	spin_lock(&hctx->lock);
+	list_add(&rq->queuelist, &hctx->dispatch);
+	spin_unlock(&hctx->lock);
+
+	blk_mq_run_hw_queue(hctx, false);
+}
+
 static void __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 					struct request *rq,
 					blk_qc_t *cookie, bool may_sleep)

@@ -1499,15 +1509,17 @@ static void __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 	switch (ret) {
 	case BLK_STS_OK:
 		*cookie = new_cookie;
-		return;
+		break;
 	case BLK_STS_RESOURCE:
 		__blk_mq_requeue_request(rq);
-		goto insert;
+		blk_mq_direct_dispatch(hctx, rq);
+		break;
 	default:
 		*cookie = BLK_QC_T_NONE;
 		blk_mq_end_request(rq, ret);
-		return;
+		break;
 	}
+	return;
 
 insert:
 	blk_mq_sched_insert_request(rq, false, run_queue, false, may_sleep);

Hello Ming,

This patch changes the behavior of blk_mq_try_issue_directly() if a scheduler
has been configured and .queue_rq() returns BLK_STS_RESOURCE, namely by skipping
the e->type->ops.mq.insert_requests() call. Sorry but I don't think this is what
we want.

It does not change behaviour for scheduler, please see
blk_mq_sched_bypass_insert() which is called from
blk_mq_sched_insert_request().

-- 
Ming