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Date:   Wed, 3 May 2023 08:56:16 -0600
From:   Keith Busch <kbusch@kernel.org>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Keith Busch <kbusch@meta.com>, linux-nvme@lists.infradead.org,
        linux-block@vger.kernel.org, joshi.k@samsung.com, axboe@kernel.dk,
        xiaoguang.wang@linux.alibaba.com
Subject: Re: [RFC 3/3] nvme: create special request queue for cdev
Message-ID: <ZFJ2EP/vGOSb1TAN@kbusch-mbp.dhcp.thefacebook.com>
References: <20230501153306.537124-1-kbusch@meta.com>
 <20230501153306.537124-4-kbusch@meta.com>
 <20230503050457.GB19301@lst.de>
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On Wed, May 03, 2023 at 07:04:57AM +0200, Christoph Hellwig wrote:
> On Mon, May 01, 2023 at 08:33:06AM -0700, Keith Busch wrote:
> > From: Keith Busch <kbusch@kernel.org>
> > 
> > The cdev only services passthrough commands which don't merge, track
> > stats, or need accounting. Give it a special request queue with all
> > these options cleared so that we're not adding overhead for it.
> 
> Why can't we always skip these for passthrough commands on any queue
> with a little bit of core code?

A special queue without a gendisk was a little easier to ensure
it's not subscribed to any rq_qos features, iolatency, wbt,
blkthrottle. We might be able to add more blk_rq_is_passthrough()
for things we want to skip and get the same benefit. I'll look into
it.