From: Keith Busch <kbusch@kernel.org>
To: Mohamed Khalfella <mkhalfella@purestorage.com>
Cc: Bart Van Assche <bvanassche@acm.org>,
Chaitanya Kulkarni <kch@nvidia.com>,
Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
Sagi Grimberg <sagi@grimberg.me>,
Casey Chen <cachen@purestorage.com>,
Yuanyuan Zhong <yzhong@purestorage.com>,
Hannes Reinecke <hare@suse.de>, Ming Lei <ming.lei@redhat.com>,
Waiman Long <llong@redhat.com>, Hillf Danton <hdanton@sina.com>,
linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] block: Use RCU in blk_mq_[un]quiesce_tagset() instead of set->tag_list_lock
Date: Fri, 5 Dec 2025 11:11:23 -0700 [thread overview]
Message-ID: <aTMgS0njg-R-T0pT@kbusch-mbp> (raw)
In-Reply-To: <20251205163926.GI2376676-mkhalfella@purestorage.com>
On Fri, Dec 05, 2025 at 08:39:26AM -0800, Mohamed Khalfella wrote:
> Why sychronize_rcu() is intolerable in this blk_mq_del_queue_tag_set()?
> This code is not performance sensitive, right?
synchronize_rcu() gets expensive on servers with many CPUs. While this
is not a fast path, I think adding it here would still be harmful, if
only just to testing when devices are frequently created and deleted.
> Looking at the code again, I _think_ synchronize_rcu() along with
> INIT_LIST_HEAD(&q->tag_set_list) can be deleted. I do not see usecase
> where "q" is re-added to a tagset after it is deleted from one.
> Also, "q" is freed in blk_free_queue() after end of RCU grace period.
I think you could skip the synchronize since the queue's memory free is
done in blk_free_queue_rcu from a call_rcu() callback.
next prev parent reply other threads:[~2025-12-05 18:11 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-04 18:11 [PATCH 0/1] Use RCU in blk_mq_[un]quiesce_tagset() instead of set->tag_list_lock Mohamed Khalfella
2025-12-04 18:11 ` [PATCH 1/1] block: " Mohamed Khalfella
2025-12-04 18:22 ` Bart Van Assche
2025-12-04 18:42 ` Mohamed Khalfella
2025-12-04 19:06 ` Bart Van Assche
2025-12-04 19:15 ` Mohamed Khalfella
2025-12-04 19:31 ` Bart Van Assche
2025-12-04 19:57 ` Mohamed Khalfella
2025-12-04 20:24 ` Bart Van Assche
2025-12-04 21:26 ` Keith Busch
2025-12-04 23:22 ` Bart Van Assche
2025-12-05 1:32 ` Keith Busch
2025-12-05 2:52 ` Bart Van Assche
2025-12-05 16:39 ` Mohamed Khalfella
2025-12-05 18:11 ` Keith Busch [this message]
2025-12-08 19:22 ` Bart Van Assche
2025-12-04 19:02 ` Mohamed Khalfella
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