Re: [PATCH 1/3] nvme/pci: Start request after doorbell ring

Jens Axboe
2017-12-21T21:01:44Z

On 12/21/17 2:02 PM, Keith Busch wrote:
> On Thu, Dec 21, 2017 at 01:53:44PM -0700, Jens Axboe wrote:
>> Turns out that wasn't what patch 2 was. And the code is right there
>> above as well, and under the q_lock, so I guess that race doesn't
>> exist.
>>
>> But that does bring up the fact if we should always be doing the
>> nvme_process_cq(nvmeq) after IO submission. For direct/hipri IO,
>> maybe it's better to make the submission path faster and skip it?
>
> Yes, I am okay to remove the opprotunistic nvme_process_cq in the
> submission path. Even under deeply queued IO, I've not seen this provide
> any measurable benefit.

I haven't either, but curious if others had. It's mostly just extra
overhead, I haven't seen it provide a latency reduction of any kind.

--
Jens Axboe