linux-kernel - [PATCH V2 2/2] block: move 'q_usage_counter' into front of 'request

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Message-Id: <20200902122643.634143-3-ming.lei@redhat.com>
Date:   Wed,  2 Sep 2020 20:26:43 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Cc:     Ming Lei <ming.lei@...hat.com>, Sagi Grimberg <sagi@...mberg.me>,
        Tejun Heo <tj@...nel.org>, Christoph Hellwig <hch@....de>,
        Jens Axboe <axboe@...nel.dk>,
        Bart Van Assche <bvanassche@....org>
Subject: [PATCH V2 2/2] block: move 'q_usage_counter' into front of 'request_queue'

The field of 'q_usage_counter' is always fetched in fast path of every
block driver, and move it into front of 'request_queue', so it can be
fetched into 1st cacheline of 'request_queue' instance.

Cc: Sagi Grimberg <sagi@...mberg.me>
Cc: Tejun Heo <tj@...nel.org>
Cc: Christoph Hellwig <hch@....de>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: Bart Van Assche <bvanassche@....org>
Signed-off-by: Ming Lei <ming.lei@...hat.com>
---
 include/linux/blkdev.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index d0d61bc81615..7575fa0aae6e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -397,6 +397,8 @@ struct request_queue {
 	struct request		*last_merge;
 	struct elevator_queue	*elevator;
 
+	struct percpu_ref	q_usage_counter;
+
 	struct blk_queue_stats	*stats;
 	struct rq_qos		*rq_qos;
 
@@ -567,7 +569,6 @@ struct request_queue {
 	 * percpu_ref_kill() and percpu_ref_reinit().
 	 */
 	struct mutex		mq_freeze_lock;
-	struct percpu_ref	q_usage_counter;
 
 	struct blk_mq_tag_set	*tag_set;
 	struct list_head	tag_set_list;
-- 
2.25.2