Re: [PATCH 0/3] DAPL support on s390x platform

[Yishai Hadas <yishaih-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>]

On 11/12/2014 1:22 AM, Roland Dreier wrote:
> On Wed, Nov 5, 2014 at 7:04 AM, Utz Bacher <utz.bacher-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org> wrote:
>> (B) Status of patches
>> 1. kernel code -- the new system call: reviewed, acked and accepted by the
>> s390x maintainer Martin Schwidefsky (2014/10/13), so we will have that
>> system call in the s390x kernel.
>> 2. libibverbs -- define barriers on s390x: Looking for your feedback. We
>> understand there have been no general objections so far.
>> 3. libmlx4 -- provide MMIO abstraction: reviewed by the Mellanox
>> maintainers and we understand they would apply this once you give the go
>> for the overall set.
>> Previously, a patch to DAPL to build on s390x has been accepted already
>> (Arlin Davis, 2014/09/02).
>>
>>    We gave your concern on MMIO handling on s390x serious consideration from
>> various angles, but the page fault handler does not appear workable. OTOH,
>> Mellanox is fine with the MMIO abstraction in libmlx4, and we didn't hear
>> of significant other concerns. With that, could you please consider the
>> patch set again to add s390x to the list of supported platforms? Happy to
>> repost the patches for convenience.
>
> If Mellanox is willing to take on the maintenance burden of changing
> all MMIO access to an inline function, and if you're willing to take
> on the burden of knowing that every new adapter you support means
> tracking down and convincing the maintainer of the driver library,
> then I'm OK with adding the simple barrier patch to libibverbs.  Could
> you please send the latest version of that patch to me?
>

The libmlx4 patch should pass some performance regression before it can 
be approved, this task is in progress in our side.

> It does seem a little strange to be adding a new system call to
> simulate kernel bypass, but I guess you do what you gotta do...
>
>   - R.
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