[PATCH 10/12] blk-mq: add a new blk_mq_complete_request_remote API

[Christoph Hellwig <hch@lst.de>]

This is a variant of blk_mq_complete_request_remote that only completes
the request if it needs to be bounced to another CPU or a softirq.  If
the request can be completed locally the function returns false and lets
the driver complete it without requring and indirect function call.

Suggestions for a better name welcome.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-mq.c         | 45 ++++++++++++++++++++++++------------------
 include/linux/blk-mq.h |  1 +
 2 files changed, 27 insertions(+), 19 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f83c81566de904..31d4bdd5bdb7bd 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -632,8 +632,11 @@ static int blk_softirq_cpu_dead(unsigned int cpu)
 	return 0;
 }
 
-static void __blk_mq_complete_request(struct request *rq)
+
+static void __blk_mq_complete_request_remote(void *data)
 {
+	struct request *rq = data;
+
 	/*
 	 * For most of single queue controllers, there is only one irq vector
 	 * for handling I/O completion, and the only irq's affinity is set
@@ -649,11 +652,6 @@ static void __blk_mq_complete_request(struct request *rq)
 		rq->q->mq_ops->complete(rq);
 }
 
-static void __blk_mq_complete_request_remote(void *data)
-{
-	__blk_mq_complete_request(data);
-}
-
 static inline bool blk_mq_complete_need_ipi(struct request *rq)
 {
 	int cpu = raw_smp_processor_id();
@@ -672,14 +670,7 @@ static inline bool blk_mq_complete_need_ipi(struct request *rq)
 	return cpu_online(rq->mq_ctx->cpu);
 }
 
-/**
- * blk_mq_complete_request - end I/O on a request
- * @rq:		the request being processed
- *
- * Description:
- *	Complete a request by scheduling the ->complete_rq operation.
- **/
-void blk_mq_complete_request(struct request *rq)
+bool blk_mq_complete_request_remote(struct request *rq)
 {
 	WRITE_ONCE(rq->state, MQ_RQ_COMPLETE);
 
@@ -687,10 +678,8 @@ void blk_mq_complete_request(struct request *rq)
 	 * For a polled request, always complete locallly, it's pointless
 	 * to redirect the completion.
 	 */
-	if (rq->cmd_flags & REQ_HIPRI) {
-		rq->q->mq_ops->complete(rq);
-		return;
-	}
+	if (rq->cmd_flags & REQ_HIPRI)
+		return false;
 
 	if (blk_mq_complete_need_ipi(rq)) {
 		rq->csd.func = __blk_mq_complete_request_remote;
@@ -698,8 +687,26 @@ void blk_mq_complete_request(struct request *rq)
 		rq->csd.flags = 0;
 		smp_call_function_single_async(rq->mq_ctx->cpu, &rq->csd);
 	} else {
-		__blk_mq_complete_request(rq);
+		if (rq->q->nr_hw_queues > 1)
+			return false;
+		blk_mq_trigger_softirq(rq);
 	}
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(blk_mq_complete_request_remote);
+
+/**
+ * blk_mq_complete_request - end I/O on a request
+ * @rq:		the request being processed
+ *
+ * Description:
+ *	Complete a request by scheduling the ->complete_rq operation.
+ **/
+void blk_mq_complete_request(struct request *rq)
+{
+	if (!blk_mq_complete_request_remote(rq))
+		rq->q->mq_ops->complete(rq);
 }
 EXPORT_SYMBOL(blk_mq_complete_request);
 
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 8e6ab766aef76e..1641ec6cd7e551 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -504,6 +504,7 @@ void blk_mq_requeue_request(struct request *rq, bool kick_requeue_list);
 void blk_mq_kick_requeue_list(struct request_queue *q);
 void blk_mq_delay_kick_requeue_list(struct request_queue *q, unsigned long msecs);
 void blk_mq_complete_request(struct request *rq);
+bool blk_mq_complete_request_remote(struct request *rq);
 bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list,
 			   struct bio *bio, unsigned int nr_segs);
 bool blk_mq_queue_stopped(struct request_queue *q);
-- 
2.26.2