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SubjectRe: [PATCH 3/3] NVMe: Convert to blk-mq
Den 22-10-2013 18:55, Keith Busch skrev:
> On Fri, 18 Oct 2013, Matias Bjørling wrote:
>> On 10/18/2013 05:13 PM, Keith Busch wrote:
>>> On Fri, 18 Oct 2013, Matias Bjorling wrote:
>>>> The nvme driver implements itself as a bio-based driver. This
>>>> primarily
>>>> because of high lock congestion for high-performance nvm devices. To
>>>> remove the congestion within the traditional block layer, a
>>>> multi-queue
>>>> block layer is being implemented.
>
>>>> - result = nvme_map_bio(nvmeq, iod, bio, dma_dir, psegs);
>>>> - if (result <= 0)
>>>> + if (nvme_map_rq(nvmeq, iod, rq, dma_dir))
>>>> goto free_cmdid;
>>>> - length = result;
>>>>
>>>> - cmnd->rw.command_id = cmdid;
>>>> + length = blk_rq_bytes(rq);
>>>> +
>>>> + cmnd->rw.command_id = rq->tag;
>>>
>>> The command ids have to be unique on a submission queue. Since each
>>> namespace's blk-mq has its own 'tags' used as command ids here but
>>> share
>>> submission queues, what's stopping the tags for commands sent to
>>> namespace
>>> 1 from clashing with tags for namespace 2?
>>>
>>> I think this would work better if one blk-mq was created per device
>>> rather than namespace. It would fix the tag problem above and save a
>>> lot of memory potentially wasted on millions of requests allocated that
>>> can't be used.
>>
>> You're right. I didn't see the connection. In v3 I'll push struct
>> request_queue to nvme_dev and map the queues appropriately. It will
>> also fix the command id issues.
>
> Just anticipating a possible issue with the suggestion. Will this
> separate
> the logical block size from the request_queue? Each namespace can have
> a different format, so the block size and request_queue can't be tied
> together like it currently is for this to work.

If only a couple of different logical sizes are to be expected (1-4), we
can keep a list of already initialized request queues, and use the one
that match an already initialized?

Axboe, do you know of a better solution?
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