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Date:   Fri, 12 May 2023 16:14:16 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Ming Lei <ming.lei@redhat.com>, linux-block@vger.kernel.org,
        Guangwu Zhang <guazhang@redhat.com>,
        Yu Kuai <yukuai1@huaweicloud.com>
Subject: Re: [PATCH] blk-mq: don't queue passthrough request into scheduler
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On Fri, May 12, 2023 at 04:12:42PM -0700, Christoph Hellwig wrote:
> On Fri, May 12, 2023 at 03:31:39PM -0600, Jens Axboe wrote:
> > That's fine for telling error handling, probing etc apart from "normal"
> > IO, but it doesn't solve the problem at hand which is assuming that
> > anything inserted into the scheduler has a bio.
> 
> I think this is fine.  Passthrough requests should never go to the
> scheduler, that's not where they blong.  Non-passthrough request always
> have a bio.

.. except for the flushes generated by block/blk-flush.c.  Those do not
enter the I/O schedule either.  That being said saying every request
has to have a bio might be a good thing some day.  Totally indepent of
the fact that schedulers have no business touching passthrough requests.