linux-kernel - [PATCH 2/3] blk-mq: clear 'active_queues' immediately when 'nr

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Date:   Sat, 26 Dec 2020 18:28:07 +0800
From:   Yu Kuai <yukuai3@...wei.com>
To:     <axboe@...nel.dk>
CC:     <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <yukuai3@...wei.com>, <yi.zhang@...wei.com>,
        <zhangxiaoxu5@...wei.com>
Subject: [PATCH 2/3] blk-mq: clear 'active_queues' immediately when 'nr_active' is decreased to 0

Currently 'active_queues' is cleared when there is no more IO in 5
secondes. Thus if multiple hardware queues share a tag set, and
some queues occasionally issue small amount of IO, some queues might
can't get enough tags while the utilization rate of total tags is
less than 100% because 'active_queues' is never decreased.

Thus clear 'active_queues' immediately when 'nr_active' is
decreased to 0.

Signed-off-by: Hou Tao <houtao1@...wei.com>
Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/blk-mq.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.h b/block/blk-mq.h
index f7212bacfa56..228c5c442be4 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -212,8 +212,10 @@ static inline void __blk_mq_dec_active_requests(struct blk_mq_hw_ctx *hctx)
 {
 	if (blk_mq_is_sbitmap_shared(hctx->flags))
 		atomic_dec(&hctx->queue->nr_active_requests_shared_sbitmap);
-	else if (!atomic_dec_return(&hctx->nr_active))
+	else if (!atomic_dec_return(&hctx->nr_active)) {
+		blk_mq_tag_idle(hctx);
 		blk_mq_dtag_idle(hctx);
+	}
 }
 
 static inline int __blk_mq_active_requests(struct blk_mq_hw_ctx *hctx)
-- 
2.25.4