linux-kernel - [PATCH V6 2/5] blk-mq-sched: move actual dispatching into one helper

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Message-Id: <20171009112424.30524-3-ming.lei@redhat.com>
Date:   Mon,  9 Oct 2017 19:24:21 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Jens Axboe <axboe@...com>, linux-block@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com
Cc:     Bart Van Assche <bart.vanassche@...disk.com>,
        Laurence Oberman <loberman@...hat.com>,
        Paolo Valente <paolo.valente@...aro.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Tom Nguyen <tom81094@...il.com>, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, Omar Sandoval <osandov@...com>,
        Ming Lei <ming.lei@...hat.com>
Subject: [PATCH V6 2/5] blk-mq-sched: move actual dispatching into one helper

So that it becomes easy to support to dispatch from sw queue in the
following patch.

No functional change.

Reviewed-by: Bart Van Assche <bart.vanassche@....com>
Reviewed-by: Omar Sandoval <osandov@...com>
Suggested-by: Christoph Hellwig <hch@....de> # for simplifying dispatch logic
Signed-off-by: Ming Lei <ming.lei@...hat.com>
---
 block/blk-mq-sched.c | 43 ++++++++++++++++++++++++-------------------
 1 file changed, 24 insertions(+), 19 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index eca011fdfa0e..be29ba849408 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -89,12 +89,26 @@ static bool blk_mq_sched_restart_hctx(struct blk_mq_hw_ctx *hctx)
 	return false;
 }
 
+static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
+{
+	struct request_queue *q = hctx->queue;
+	struct elevator_queue *e = q->elevator;
+	LIST_HEAD(rq_list);
+
+	do {
+		struct request *rq = e->type->ops.mq.dispatch_request(hctx);
+
+		if (!rq)
+			break;
+		list_add(&rq->queuelist, &rq_list);
+	} while (blk_mq_dispatch_rq_list(q, &rq_list));
+}
+
 void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 {
 	struct request_queue *q = hctx->queue;
 	struct elevator_queue *e = q->elevator;
 	const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request;
-	bool do_sched_dispatch = true;
 	LIST_HEAD(rq_list);
 
 	/* RCU or SRCU read lock is needed before checking quiesced flag */
@@ -122,30 +136,21 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 	 * scheduler, we can no longer merge or sort them. So it's best to
 	 * leave them there for as long as we can. Mark the hw queue as
 	 * needing a restart in that case.
+	 *
+	 * We want to dispatch from the scheduler if there was nothing
+	 * on the dispatch list or we were able to dispatch from the
+	 * dispatch list.
 	 */
 	if (!list_empty(&rq_list)) {
 		blk_mq_sched_mark_restart_hctx(hctx);
-		do_sched_dispatch = blk_mq_dispatch_rq_list(q, &rq_list);
-	} else if (!has_sched_dispatch) {
+		if (blk_mq_dispatch_rq_list(q, &rq_list) && has_sched_dispatch)
+			blk_mq_do_dispatch_sched(hctx);
+	} else if (has_sched_dispatch) {
+		blk_mq_do_dispatch_sched(hctx);
+	} else {
 		blk_mq_flush_busy_ctxs(hctx, &rq_list);
 		blk_mq_dispatch_rq_list(q, &rq_list);
 	}
-
-	/*
-	 * We want to dispatch from the scheduler if there was nothing
-	 * on the dispatch list or we were able to dispatch from the
-	 * dispatch list.
-	 */
-	if (do_sched_dispatch && has_sched_dispatch) {
-		do {
-			struct request *rq;
-
-			rq = e->type->ops.mq.dispatch_request(hctx);
-			if (!rq)
-				break;
-			list_add(&rq->queuelist, &rq_list);
-		} while (blk_mq_dispatch_rq_list(q, &rq_list));
-	}
 }
 
 bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
-- 
2.9.5