linux-kernel - Re: [PATCH v15 7/9] nvmet-passthru: Add passthru code to process commands

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Message-ID: <20200720231701.GA682160@dhcp-10-100-145-180.wdl.wdc.com>
Date:   Mon, 20 Jul 2020 16:17:01 -0700
From:   Keith Busch <kbusch@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Sagi Grimberg <sagi@...mberg.me>, Christoph Hellwig <hch@....de>,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        Jens Axboe <axboe@...com>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [PATCH v15 7/9] nvmet-passthru: Add passthru code to process
 commands

On Mon, Jul 20, 2020 at 05:01:19PM -0600, Logan Gunthorpe wrote:
> On 2020-07-20 4:35 p.m., Sagi Grimberg wrote:
>
> > passthru commands are in essence REQ_OP_DRV_IN/REQ_OP_DRV_OUT, which
> > means that the driver shouldn't need the ns at all. So if you have a
> > dedicated request queue (mapped to the I/O tagset), you don't need the
> > ns->queue and we can lose the ns lookup altogether.

We still need a request_queue to dispatch the command. I guess you could
make a generic one for the controller that isn't tied to a namespace,
but we lose the fair shared tag allocation.
 
> Thanks, that helps clarify things a bit, but which xarray were you
> talking about

That was something that was replacing the list lookup:

  http://lists.infradead.org/pipermail/linux-nvme/2020-July/018242.html