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Date:   Wed, 10 Nov 2021 13:58:56 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        linux-block@vger.kernel.org, linux-scsi@vger.kernel.org,
        linux-nvme@lists.infradead.org
Subject: Re: sorting out the freeze / quiesce mess
Message-ID: <20211110125856.GA25614@lst.de>
References: <20211110091407.GA8396@lst.de> <YYuQ9mhHtDNDVFQ3@T590>
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On Wed, Nov 10, 2021 at 05:29:26PM +0800, Ming Lei wrote:
> On Wed, Nov 10, 2021 at 10:14:07AM +0100, Christoph Hellwig wrote:
> > Hi Jens and Ming,
> > 
> > I've been looking into properly supporting queue freezing for bio based
> > drivers (that is only release q_usage_counter on bio completion for them).
> > And the deeper I look into the code the more I'm confused by us having
> > the blk_mq_quiesce* interface in addition to blk_freeze_queue.  What
> > is a good reason to do a quiesce separately from a freeze?
> 
> freeze can make sure that all requests are done, quiesce can make sure that
> dispatch critical area(covered by hctx lock/unlock) is done.

Yeah, but why do we need to still call quiesce after we just did a
freeze, which is about half of the users?