linux-kernel - Re: [PATCH 1/1] block: Use RCU in blk_mq_[un]quiesce_tagset() instead of set->tag_list

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Message-ID: <71e9950f-ace7-4570-a604-ceca347eea20@acm.org>
Date: Thu, 4 Dec 2025 09:06:47 -1000
From: Bart Van Assche <bvanassche@....org>
To: Mohamed Khalfella <mkhalfella@...estorage.com>
Cc: Chaitanya Kulkarni <kch@...dia.com>, Christoph Hellwig <hch@....de>,
 Jens Axboe <axboe@...nel.dk>, Keith Busch <kbusch@...nel.org>,
 Sagi Grimberg <sagi@...mberg.me>, Casey Chen <cachen@...estorage.com>,
 Yuanyuan Zhong <yzhong@...estorage.com>, Hannes Reinecke <hare@...e.de>,
 Ming Lei <ming.lei@...hat.com>, Waiman Long <llong@...hat.com>,
 Hillf Danton <hdanton@...a.com>, linux-nvme@...ts.infradead.org,
 linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] block: Use RCU in blk_mq_[un]quiesce_tagset() instead
 of set->tag_list_lock

On 12/4/25 8:42 AM, Mohamed Khalfella wrote:
> Is blk_mq_del_queue_tag_set() performance sensitive such that it can not
> take synchronize_rcu()? It is not in IO codepath, right?

Introducing a new synchronize_rcu() call almost always slows down some 
workload so it should be avoided if possible.

 > I can not think of an easy way to do that. Suggestions are welcomed.

I can't find the implementation of nvme_dev_disable_locked(). What
kernel tree does your patch apply to?

$ git grep -w nvme_dev_disable_locked axboe-block/for-next | wc -l
0

Thanks,

Bart.