[PATCH V3 1/4] 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. To make the code clearer, introduce new helpers
blk_mq_make_decision and enum mq_decision.

Signed-off-by: Jianchao Wang <jianchao.w.wang@xxxxxxxxxx>
---
 block/blk-mq.c     | 104 ++++++++++++++++++++++++++++++-----------------------
 block/blk-mq.c.rej |  60 +++++++++++++++++++++++++++++++
 2 files changed, 120 insertions(+), 44 deletions(-)
 create mode 100644 block/blk-mq.c.rej

diff --git a/block/blk-mq.c b/block/blk-mq.c
index dcf10e3..0f6328b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1711,7 +1711,6 @@ 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;
 		break;
 	case BLK_STS_RESOURCE:
 	case BLK_STS_DEV_RESOURCE:
@@ -1720,86 +1719,103 @@ 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,
+enum mq_decision {
+	MQ_INSERT_QUEUE,
+	MQ_END_REQUEST,
+	MQ_DO_NOTHING,
+};
+
+static inline enum mq_decision
+	blk_mq_make_dicision(blk_status_t ret, bool bypass_insert)
+{
+	enum mq_decision dec;
+
+	switch(ret) {
+	case BLK_STS_OK:
+		dec = MQ_DO_NOTHING;
+		break;
+	case BLK_STS_DEV_RESOURCE:
+	case BLK_STS_RESOURCE:
+		dec = bypass_insert ? MQ_DO_NOTHING : MQ_INSERT_QUEUE;
+		break;
+	default:
+		dec = bypass_insert ? MQ_DO_NOTHING : MQ_END_REQUEST;
+		break;
+	}
+
+	return dec;
+}
+
+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)
 {
 	struct request_queue *q = rq->q;
 	bool run_queue = true;
+	enum mq_decision dec;
+	blk_status_t ret = BLK_STS_RESOURCE;
+	int srcu_idx;
 
+	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;
+		goto out_unlock;
 	}
 
 	if (q->elevator && !bypass_insert)
-		goto insert;
+		goto out_unlock;
 
 	if (!blk_mq_get_dispatch_budget(hctx))
-		goto insert;
+		goto out_unlock;
 
 	if (!blk_mq_get_driver_tag(rq)) {
 		blk_mq_put_dispatch_budget(hctx);
-		goto insert;
+		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_issue_directly(hctx, rq, cookie);
+out_unlock:
+	hctx_unlock(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)
+	dec = blk_mq_make_dicision(ret, bypass_insert);
+	switch(dec) {
+	case MQ_INSERT_QUEUE:
+		blk_mq_sched_insert_request(rq, false, run_queue, false);
+		break;
+	case MQ_END_REQUEST:
 		blk_mq_end_request(rq, ret);
+		break;
+	default:
+		return ret;
+	}
 
-	hctx_unlock(hctx, srcu_idx);
+	return BLK_STS_OK;
 }
 
 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 +1937,13 @@ 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);
diff --git a/block/blk-mq.c.rej b/block/blk-mq.c.rej
new file mode 100644
index 0000000..7813cd9
--- /dev/null
+++ b/block/blk-mq.c.rej
@@ -0,0 +1,60 @@
+--- block/blk-mq.c
++++ block/blk-mq.c
+@@ -1728,13 +1728,14 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
+ }
+ 
+ enum mq_decision {
++       MQ_INSERT_DISPATCH,
+        MQ_INSERT_QUEUE,
+        MQ_END_REQUEST,
+        MQ_DO_NOTHING,
+ };
+ 
+-static inline enum mq_decision
+-       blk_mq_make_dicision(blk_status_t ret, bool bypass_insert)
++static inline enum mq_decision blk_mq_make_dicision(blk_status_t ret,
++               bool bypass_insert, bool force_insert)
+ {
+        enum mq_decision dec;
+ 
+@@ -1744,7 +1745,10 @@ static inline enum mq_decision
+                break;
+        case BLK_STS_DEV_RESOURCE:
+        case BLK_STS_RESOURCE:
+-               dec = bypass_insert ? MQ_DO_NOTHING : MQ_INSERT_QUEUE;
++               if (force_insert)
++                       dec = bypass_insert ? MQ_INSERT_DISPATCH : MQ_INSERT_QUEUE;
++               else
++                       dec = bypass_insert ? MQ_DO_NOTHING : MQ_INSERT_QUEUE;
+                break;
+        default:
+                dec = bypass_insert ? MQ_DO_NOTHING : MQ_END_REQUEST;
+@@ -1760,7 +1764,7 @@ static blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
+                                                bool bypass_insert)
+ {
+        struct request_queue *q = rq->q;
+-       bool run_queue = true;
++       bool run_queue = true, force_insert = false;
+        enum mq_decision dec;
+        blk_status_t ret = BLK_STS_RESOURCE;
+        int srcu_idx;
+@@ -1775,7 +1779,7 @@ static blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
+         */
+        if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)) {
+                run_queue = false;
+-               bypass_insert = false;
++               force_insert = true;
+                goto out_unlock;
+        }
+ 
+@@ -1795,7 +1799,10 @@ static blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
+        hctx_unlock(hctx, srcu_idx);
+ 
+        dec = blk_mq_make_dicision(ret, bypass_insert);
+       switch(pos) {
++       case MQ_INSERT_DISPATCH:
++               blk_mq_request_bypass_insert(rq, run_queue);
++               break;
+        case MQ_INSERT_QUEUE:
+                blk_mq_sched_insert_request(rq, false, run_queue, false);
+                break;
-- 
2.7.4