[PATCH V2 1/3] blk-mq: refactor the code of issue request directly

[Jianchao Wang]

Merge blk_mq_try_issue_directly and __blk_mq_try_issue_directly
into one interface which is able to handle the return value from
.queue_rq callback. Due to we can only issue directly w/o io
scheduler, so remove the blk_mq_get_driver_tag.

Signed-off-by: Jianchao Wang <jianchao.w.wang@xxxxxxxxxx>
---
 block/blk-mq.c | 109 ++++++++++++++++++++++++++-------------------------------
 1 file changed, 50 insertions(+), 59 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index dcf10e3..a81d2ca 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1700,8 +1700,6 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
 	blk_qc_t new_cookie;
 	blk_status_t ret;
 
-	new_cookie = request_to_qc_t(hctx, rq);
-
 	/*
 	 * For OK queue, we are done. For error, caller may kill it.
 	 * Any other error (busy), just add it to our list as we
@@ -1711,7 +1709,7 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
 	switch (ret) {
 	case BLK_STS_OK:
 		blk_mq_update_dispatch_busy(hctx, false);
-		*cookie = new_cookie;
+		new_cookie = request_to_qc_t(hctx, rq);
 		break;
 	case BLK_STS_RESOURCE:
 	case BLK_STS_DEV_RESOURCE:
@@ -1720,86 +1718,79 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
 		break;
 	default:
 		blk_mq_update_dispatch_busy(hctx, false);
-		*cookie = BLK_QC_T_NONE;
+		new_cookie = BLK_QC_T_NONE;
 		break;
 	}
 
+	if (cookie)
+		*cookie = new_cookie;
 	return ret;
 }
 
-static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
+/*
+ * When the bypass is true, the caller is responsible for handling the
+ * request if it is not issued. The only exception is that io scheduler
+ * is set.
+ */
+static blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 						struct request *rq,
 						blk_qc_t *cookie,
-						bool bypass_insert)
+						bool bypass)
 {
 	struct request_queue *q = rq->q;
-	bool run_queue = true;
+	blk_status_t ret = BLK_STS_OK;
+	bool insert = true;
+	int srcu_idx;
+
+	if (q->elevator)
+		goto out;
 
+	hctx_lock(hctx, &srcu_idx);
 	/*
-	 * RCU or SRCU read lock is needed before checking quiesced flag.
+	 * hctx_lock is needed before checking quiesced flag.
 	 *
-	 * When queue is stopped or quiesced, ignore 'bypass_insert' from
-	 * blk_mq_request_issue_directly(), and return BLK_STS_OK to caller,
-	 * and avoid driver to try to dispatch again.
+	 * When queue is stopped or quiesced, ignore 'bypass', insert and return
+	 * BLK_STS_OK to caller, and avoid driver to try to dispatch again.
 	 */
-	if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)) {
-		run_queue = false;
-		bypass_insert = false;
-		goto insert;
-	}
-
-	if (q->elevator && !bypass_insert)
-		goto insert;
+	if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q))
+		goto out_unlock;
 
-	if (!blk_mq_get_dispatch_budget(hctx))
-		goto insert;
-
-	if (!blk_mq_get_driver_tag(rq)) {
-		blk_mq_put_dispatch_budget(hctx);
-		goto insert;
+	if (!blk_mq_get_dispatch_budget(hctx)) {
+		insert = !bypass;
+		ret = bypass ? BLK_STS_RESOURCE : BLK_STS_OK;
+		goto out_unlock;
 	}
 
-	return __blk_mq_issue_directly(hctx, rq, cookie);
-insert:
-	if (bypass_insert)
-		return BLK_STS_RESOURCE;
-
-	blk_mq_sched_insert_request(rq, false, run_queue, false);
-	return BLK_STS_OK;
-}
-
-static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
-		struct request *rq, blk_qc_t *cookie)
-{
-	blk_status_t ret;
-	int srcu_idx;
-
-	might_sleep_if(hctx->flags & BLK_MQ_F_BLOCKING);
-
-	hctx_lock(hctx, &srcu_idx);
-
-	ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false);
-	if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE)
-		blk_mq_sched_insert_request(rq, false, true, false);
-	else if (ret != BLK_STS_OK)
-		blk_mq_end_request(rq, ret);
+	ret = __blk_mq_issue_directly(hctx, rq, cookie);
+	switch(ret) {
+	case BLK_STS_OK:
+		insert = false;
+		break;
+	case BLK_STS_DEV_RESOURCE:
+	case BLK_STS_RESOURCE:
+		insert = !bypass;
+		break;
+	default:
+		if (!bypass)
+			blk_mq_end_request(rq, ret);
+		insert = false;
+		break;
+	}
 
+out_unlock:
 	hctx_unlock(hctx, srcu_idx);
+out:
+	if (insert)
+		blk_mq_sched_insert_request(rq, false, true, false);
+	return ret;
 }
 
 blk_status_t blk_mq_request_issue_directly(struct request *rq)
 {
-	blk_status_t ret;
-	int srcu_idx;
-	blk_qc_t unused_cookie;
 	struct blk_mq_ctx *ctx = rq->mq_ctx;
 	struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(rq->q, ctx->cpu);
 
-	hctx_lock(hctx, &srcu_idx);
-	ret = __blk_mq_try_issue_directly(hctx, rq, &unused_cookie, true);
-	hctx_unlock(hctx, srcu_idx);
-
-	return ret;
+	return  blk_mq_try_issue_directly(hctx, rq, NULL, true);
 }
 
 void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
@@ -1921,13 +1912,13 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 			data.hctx = blk_mq_map_queue(q,
 					same_queue_rq->mq_ctx->cpu);
 			blk_mq_try_issue_directly(data.hctx, same_queue_rq,
-					&cookie);
+					&cookie, false);
 		}
 	} else if ((q->nr_hw_queues > 1 && is_sync) || (!q->elevator &&
 			!data.hctx->dispatch_busy)) {
 		blk_mq_put_ctx(data.ctx);
 		blk_mq_bio_to_request(rq, bio);
-		blk_mq_try_issue_directly(data.hctx, rq, &cookie);
+		blk_mq_try_issue_directly(data.hctx, rq, &cookie, false);
 	} else {
 		blk_mq_put_ctx(data.ctx);
 		blk_mq_bio_to_request(rq, bio);
-- 
2.7.4