[xenial:linux-azure][PATCH 12/15] blk-mq: issue directly if hw queue isn't busy in case of 'none'

Marcelo Henrique Cerri marcelo.cerri at canonical.com
Wed Nov 27 20:18:17 UTC 2019


From: Ming Lei <ming.lei at redhat.com>

BugLink: https://bugs.launchpad.net/bugs/1848739

In case of 'none' io scheduler, when hw queue isn't busy, it isn't
necessary to enqueue request to sw queue and dequeue it from
sw queue because request may be submitted to hw queue asap without
extra cost, meantime there shouldn't be much request in sw queue,
and we don't need to worry about effect on IO merge.

There are still some single hw queue SCSI HBAs(HPSA, megaraid_sas, ...)
which may connect high performance devices, so 'none' is often required
for obtaining good performance.

This patch improves IOPS and decreases CPU unilization on megaraid_sas,
per Kashyap's test.

Cc: Kashyap Desai <kashyap.desai at broadcom.com>
Cc: Laurence Oberman <loberman at redhat.com>
Cc: Omar Sandoval <osandov at fb.com>
Cc: Christoph Hellwig <hch at lst.de>
Cc: Bart Van Assche <bart.vanassche at wdc.com>
Cc: Hannes Reinecke <hare at suse.de>
Reported-by: Kashyap Desai <kashyap.desai at broadcom.com>
Tested-by: Kashyap Desai <kashyap.desai at broadcom.com>
Signed-off-by: Ming Lei <ming.lei at redhat.com>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
(cherry picked from commit 6ce3dd6eec114930cf2035a8bcb1e80477ed79a8)
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
---
 block/blk-mq-sched.c | 13 ++++++++++++-
 block/blk-mq.c       | 23 ++++++++++++++++++++++-
 block/blk-mq.h       |  2 ++
 3 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 1518c794a78c..45d8e861fe55 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -465,8 +465,19 @@ void blk_mq_sched_insert_requests(struct request_queue *q,
 
 	if (e && e->type->ops.mq.insert_requests)
 		e->type->ops.mq.insert_requests(hctx, list, false);
-	else
+	else {
+		/*
+		 * try to issue requests directly if the hw queue isn't
+		 * 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) {
+			blk_mq_try_issue_list_directly(hctx, list);
+			if (list_empty(list))
+				return;
+		}
 		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 691ed5f8f6d9..ea3feeab1fd0 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1768,13 +1768,16 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
 	ret = q->mq_ops->queue_rq(hctx, &bd);
 	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:
+		blk_mq_update_dispatch_busy(hctx, true);
 		__blk_mq_requeue_request(rq);
 		break;
 	default:
+		blk_mq_update_dispatch_busy(hctx, false);
 		*cookie = BLK_QC_T_NONE;
 		break;
 	}
@@ -1857,6 +1860,23 @@ blk_status_t blk_mq_request_issue_directly(struct request *rq)
 	return ret;
 }
 
+void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
+		struct list_head *list)
+{
+	while (!list_empty(list)) {
+		blk_status_t ret;
+		struct request *rq = list_first_entry(list, struct request,
+				queuelist);
+
+		list_del_init(&rq->queuelist);
+		ret = blk_mq_request_issue_directly(rq);
+		if (ret != BLK_STS_OK) {
+			list_add(&rq->queuelist, list);
+			break;
+		}
+	}
+}
+
 static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 {
 	const int is_sync = op_is_sync(bio->bi_opf);
@@ -1958,7 +1978,8 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 			blk_mq_try_issue_directly(data.hctx, same_queue_rq,
 					&cookie);
 		}
-	} else if (q->nr_hw_queues > 1 && is_sync) {
+	} 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);
diff --git a/block/blk-mq.h b/block/blk-mq.h
index c11c627ebd6d..b78cdcad7d7f 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -62,6 +62,8 @@ void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
 
 /* Used by blk_insert_cloned_request() to issue request directly */
 blk_status_t blk_mq_request_issue_directly(struct request *rq);
+void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
+				    struct list_head *list);
 
 /*
  * CPU -> queue mappings
-- 
2.20.1




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