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

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Message-ID: <be06756a-bb05-ae83-3aea-6eb97d985160@grimberg.me>
Date:   Mon, 20 Jul 2020 17:39:04 -0700
From:   Sagi Grimberg <sagi@...mberg.me>
To:     Keith Busch <kbusch@...nel.org>
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        Stephen Bates <sbates@...thlin.com>, Jens Axboe <axboe@...com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Christoph Hellwig <hch@....de>
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.
>>
>> What do you mean fair shared tag allocation?
> 
> See hctx_may_queue().

Still not following your point... this queue is yet another request
queue on the I/O tagset, e.g.

ctrl->passthru_q = blk_mq_init_queue(ctrl->tagset);