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Date:   Wed, 19 Oct 2022 09:25:35 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Sagi Grimberg <sagi@grimberg.me>
Cc:     Ming Lei <ming.lei@redhat.com>, Christoph Hellwig <hch@lst.de>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Chao Leng <lengchao@huawei.com>,
        linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
        kbusch@kernel.org, axboe@kernel.dk
Subject: Re: [PATCH v2 1/2] blk-mq: add tagset quiesce interface
Message-ID: <20221019072535.GA11402@lst.de>
References: <20221013094450.5947-1-lengchao@huawei.com> <20221013094450.5947-2-lengchao@huawei.com> <20221017133906.GA24492@lst.de> <20221017152136.GI5600@paulmck-ThinkPad-P17-Gen-1> <20221017153105.GA32509@lst.de> <20221017224115.GJ5600@paulmck-ThinkPad-P17-Gen-1> <20221018051956.GA18802@lst.de> <Y09GROYqk3FMM21W@T590> <9da048fc-71ee-cc38-a861-59acc96671fe@grimberg.me>
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On Wed, Oct 19, 2022 at 10:15:26AM +0300, Sagi Grimberg wrote:
> nvme-tcp will opportunistically try a network send directly from
> .queue_rq(), but always with MSG_DONTWAIT, so that is not a problem.
>
> nbd though can block in .queue_rq() with blocking network sends, however
> afaict nbd allocates a tagset per nbd_device, and also a request_queue
> per device, so its effectively the same if the srcu is in the tagset or
> in the request_queue.

Yes, the only multiple request_queue per tag_set cases right now
are nvme-tcp and mmc.  There have been patches from iSCSI, but they
seem to be stuck.