[GEDI] [PATCH-for-9.1 v2 2/3] migration: Remove RDMA protocol handling

[Zhijian Li (Fujitsu)]

On 28/03/2024 23:01, Peter Xu wrote:
> On Thu, Mar 28, 2024 at 11:18:04AM -0300, Fabiano Rosas wrote:
>> Philippe Mathieu-Daudé <philmd at linaro.org> writes:
>>
>>> The whole RDMA subsystem was deprecated in commit e9a54265f5
>>> ("hw/rdma: Deprecate the pvrdma device and the rdma subsystem")
>>> released in v8.2.
>>>
>>> Remove:
>>>   - RDMA handling from migration
>>>   - dependencies on libibumad, libibverbs and librdmacm
>>>
>>> Keep the RAM_SAVE_FLAG_HOOK definition since it might appears
>>> in old migration streams.
>>>
>>> Cc: Peter Xu <peterx at redhat.com>
>>> Cc: Li Zhijian <lizhijian at fujitsu.com>
>>> Acked-by: Fabiano Rosas <farosas at suse.de>
>>> Signed-off-by: Philippe Mathieu-Daudé <philmd at linaro.org>
>>
>> Just to be clear, because people raised the point in the last version,
>> the first link in the deprecation commit links to a thread comprising
>> entirely of rdma migration patches. I don't see any ambiguity on whether
>> the deprecation was intended to include migration. There's even an ack
>> from Juan.
> 
> Yes I remember that's the plan.
> 
>>
>> So on the basis of not reverting the previous maintainer's decision, my
>> Ack stands here.
>>
>> We also had pretty obvious bugs ([1], [2]) in the past that would have
>> been caught if we had any kind of testing for the feature, so I can't
>> even say this thing works currently.
>>
>> @Peter Xu, @Li Zhijian, what are your thoughts on this?
> 
> Generally I definitely agree with such a removal sooner or later, as that's
> how deprecation works, and even after Juan's left I'm not aware of any
> other new RDMA users.  Personally, I'd slightly prefer postponing it one
> more release which might help a bit of our downstream maintenance, however
> I assume that's not a blocker either, as I think we can also manage it.
> 
> IMHO it's more important to know whether there are still users and whether
> they would still like to see it around. That's also one thing I notice that
> e9a54265f533f didn't yet get acks from RDMA users that we are aware, even
> if they're rare. According to [2] it could be that such user may only rely
> on the release versions of QEMU when it broke things.
> 
> So I'm copying Yu too (while Zhijian is already in the loop), just in case
> someone would like to stand up and speak.


I admit RDMA migration was lack of testing(unit/CI test), which led to the a few
obvious bugs being noticed too late.
However I was a bit surprised when I saw the removal of the RDMA migration. I wasn't
aware that this feature has not been marked as deprecated(at least there is no
prompt to end-user).


> IMHO it's more important to know whether there are still users and whether
> they would still like to see it around.

Agree.
I didn't immediately express my opinion in V1 because I'm also consulting our
customers for this feature in the future.

Personally, I agree with Perter's idea that "I'd slightly prefer postponing it one
more release which might help a bit of our downstream maintenance"

Thanks
Zhijian

> 
> Thanks,
> 
>>
>> 1- https://lore.kernel.org/r/20230920090412.726725-1-lizhijian@fujitsu.com
>> 2- https://lore.kernel.org/r/CAHEcVy7HXSwn4Ow_Kog+Q+TN6f_kMeiCHevz1qGM-fbxBPp1hQ@mail.gmail.com
>>
>