Re: [PATCH V7 00/10] mmc: Add Command Queue support

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On 5 September 2017 at 10:10, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
> On 05/09/17 10:24, Ulf Hansson wrote:
>> [...]
>>
>>>>>
>>>>> I can send blk-mq support for legacy requests in a few days if you like, but
>>>>> I want to hear a better explanation of why you are delaying CQE support.
>>>>
>>>> That would be very nice, however be aware of that we are in the merge
>>>> window, so I am not picking new material for 4.14 from this point. I
>>>> assume you understand why.
>>>
>>> Nope.  This is new functionality - doesn't affect anyone who doesn't have a
>>> command queue engine.  Next to no chance of regressions.  Tested by several
>>> in the community.  Substantially unchanged since February.  It is not even
>>> very much code in the block driver.
>>
>> Let me make it clear, once more - I don't want to maintain more hacks
>> in mmc block layer code.
>>
>> This series add blkmq support, using a method (which may be considered
>> as intermediate) via a new change in patch1 - but only for the new CQE
>> path. That means the old legacy mmc block path is still there. So, for
>> the reason stated above - no thanks!
>
> And where is your alternative.  When I pointed out you need a way to
> arbitrate between internal partitions, you went silent again.
>
> Can't have CQE without blk-mq but can't have blk-mq because you don't
> understand it, is hardly acceptable.

Adrian, this discussion seems to lead nowhere. Can we please stop and
be constructive instead!

Regarding the arbitration issue. We have been moving forward,
re-factoring the mmc block driver code, soon also solving the problem
for the rpmb internal partition [1]. Maybe the background to why Linus
is working on mmc block re-factoring, hasn't been entirely clear.
Anyway, it's exactly because of moving closer to address these issues.

Even if the problems certainly becomes a step harder to resolve for
the boot and the general purpose partitions, it's still a path we
should try to find a solution for. Yeah, that may mean we need to
suggest changes for the generic block layer, to teach it to better
deal with these kind of devices.

Finally, I have never said the arbitration issue *must* be solved
before converting to blkmq. Only that we should avoid performance
regressions, but that of course applies to whatever changes we do.

[...]

Kind regards
Uffe

[1]
https://patchwork.kernel.org/patch/9911463/
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