linux-kernel - [PATCH V9 3/4] blk-mq: issue directly with bypass 'false' in blk_mq_sched_insert

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Date:   Wed,  5 Dec 2018 15:44:01 +0800
From:   Jianchao Wang <jianchao.w.wang@...cle.com>
To:     axboe@...nel.dk
Cc:     ming.lei@...hat.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH V9 3/4] blk-mq: issue directly with bypass 'false' in blk_mq_sched_insert_requests

It is not necessary to issue request directly with bypass 'true'
in blk_mq_sched_insert_requests and handle the non-issued requests
itself. Just set bypass to 'false' and let blk_mq_try_issue_directly
handle them totally. Remove the blk_rq_can_direct_dispatch check,
because blk_mq_try_issue_directly can handle it well.

With respect to commit_rqs hook, we only need to care about the last
request's result. If it is inserted, invoke commit_rqs. We identify
the actual result of blk_mq_try_issue_directly with outputed cookie.

Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
---
 block/blk-mq-sched.c      |  8 +++-----
 block/blk-mq.c            | 25 ++++++++-----------------
 include/linux/blk_types.h |  1 +
 3 files changed, 12 insertions(+), 22 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index f096d898..5b4d52d 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -417,12 +417,10 @@ void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx,
 		 * busy in case of 'none' scheduler, and this way may save
 		 * us one extra enqueue & dequeue to sw queue.
 		 */
-		if (!hctx->dispatch_busy && !e && !run_queue_async) {
+		if (!hctx->dispatch_busy && !e && !run_queue_async)
 			blk_mq_try_issue_list_directly(hctx, list);
-			if (list_empty(list))
-				return;
-		}
-		blk_mq_insert_requests(hctx, ctx, list);
+		else
+			blk_mq_insert_requests(hctx, ctx, list);
 	}
 
 	blk_mq_run_hw_queue(hctx, run_queue_async);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index fe92e52..0dfa269 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1899,32 +1899,23 @@ blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
 void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 		struct list_head *list)
 {
+	blk_qc_t cookie = BLK_QC_T_INVALID;
+
 	while (!list_empty(list)) {
-		blk_status_t ret;
 		struct request *rq = list_first_entry(list, struct request,
 				queuelist);
 
-		if (!blk_rq_can_direct_dispatch(rq))
-			break;
-
 		list_del_init(&rq->queuelist);
-		ret = blk_mq_request_issue_directly(rq, list_empty(list));
-		if (ret != BLK_STS_OK) {
-			if (ret == BLK_STS_RESOURCE ||
-					ret == BLK_STS_DEV_RESOURCE) {
-				list_add(&rq->queuelist, list);
-				break;
-			}
-			blk_mq_end_request(rq, ret);
-		}
+		blk_mq_try_issue_directly(hctx, rq, &cookie, false,
+				list_empty(list));
 	}
 
 	/*
-	 * If we didn't flush the entire list, we could have told
-	 * the driver there was more coming, but that turned out to
-	 * be a lie.
+	 * cookie is set to a valid value only when reqeust is issued successfully.
+	 * We only need to care about the last request's result, if it is inserted,
+	 * kick the hardware with commit_rqs hook.
 	 */
-	if (!list_empty(list) && hctx->queue->mq_ops->commit_rqs)
+	if ((cookie == BLK_QC_T_INVALID) && hctx->queue->mq_ops->commit_rqs)
 		hctx->queue->mq_ops->commit_rqs(hctx);
 }
 
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index c0ba1a0..a0a467a41 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -414,6 +414,7 @@ static inline int op_stat_group(unsigned int op)
 }
 
 typedef unsigned int blk_qc_t;
+#define BLK_QC_T_INVALID 	-2U
 #define BLK_QC_T_NONE		-1U
 #define BLK_QC_T_SHIFT		16
 #define BLK_QC_T_INTERNAL	(1U << 31)
-- 
2.7.4