Re: [PATCH V4 00/11] mmc: Add Command Queue support

Ulf Hansson
2017-08-08T10:36:18Z

On 8 August 2017 at 11:26, Adrian Hunter <adrian.hunter@intel.com> wrote:
> On 07/08/17 16:41, Ulf Hansson wrote:
>> On 21 July 2017 at 11:49, Adrian Hunter <adrian.hunter@intel.com> wrote:
>>> Hi
>>>
>>> Here is V4 of the hardware command queue patches without the software
>>> command queue patches.
>>
>> Adrian, again apologize for the delay.
>>
>> I am reviewing the series now and my intent is to provide comments on
>> each change separately during the week.
>>
>> However, a couple of overall thoughts:
>>
>> *) Could you please post some fresh performance measurements, such we
>> can get some real proof on why CMDQ is worth to be merged? If not
>> increased throughput, perhaps we can show some decreased I/O requests
>> latency!?
>
> HW CMDQ offers 25% - 50% better random multi-threaded I/O. I see a slight
> 2% drop in sequential read speed but no change to sequential write.

Great, that satisfies my request! Could you please fold in this
information in one of the change-logs, which adds supports for the
CQE?

>
>>
>> **) I have spoken to Linus W offlist - and he is still working on the
>> blkmq port. Although we first need to continue with the
>> re-factorization of the mmc block/core code, to minimize the bad
>> impact of our big mmc claim host lock. We should expect a
>> re-submission of his series quite soonish. However, it's also likely
>> that we need yet another round of re-factoring, before we can complete
>> the port to blkmq.
>>
>> ***) The reason for bringing up **), is of course because I think
>> deploying CMDQ support would be better done on top of the blkmq
>> interface as it's better suited for these kind of device types. My
>> goal is to reach a better maintenance situation, using more modern mmc
>> block code. We have spoken about this before, however of course I also
>> don't want to delay the CMDQ series. Anyway, let's move forward and
>> see what path we end up taking.
>
> There is no advantage to holding up HW CMDQ.

Maybe not.

I haven't completed the review yet, but I guess you understand my
concerns on the impact of the blkmq port.

If I can get some promises about yours support (testing/reviewing/etc)
of the blkmq port series when going forward, that would of course
impact my decision on what path to pick.

Does that sounds reasonable to you?

[...]

Kind regards
Uffe