Re: [PATCH rdma-next 00/10] Enable relaxed ordering for ULPs

Chuck Lever III
2021-04-05T23:44:09Z

> On Apr 5, 2021, at 4:07 PM, Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> On Mon, Apr 05, 2021 at 03:41:15PM +0200, Christoph Hellwig wrote:
>> On Mon, Apr 05, 2021 at 08:23:54AM +0300, Leon Romanovsky wrote:
>>> From: Leon Romanovsky <leonro@nvidia.com>
>>>
>>>> From Avihai,
>>>
>>> Relaxed Ordering is a PCIe mechanism that relaxes the strict ordering
>>> imposed on PCI transactions, and thus, can improve performance.
>>>
>>> Until now, relaxed ordering could be set only by user space applications
>>> for user MRs. The following patch series enables relaxed ordering for the
>>> kernel ULPs as well. Relaxed ordering is an optional capability, and as
>>> such, it is ignored by vendors that don't support it.
>>>
>>> The following test results show the performance improvement achieved
>>> with relaxed ordering. The test was performed on a NVIDIA A100 in order
>>> to check performance of storage infrastructure over xprtrdma:
>>
>> Isn't the Nvidia A100 a GPU not actually supported by Linux at all?
>> What does that have to do with storage protocols?
>
> I think it is a typo (or at least mit makes no sense to be talking
> about NFS with a GPU chip) Probably it should be a DGX A100 which is a
> dual socket AMD server with alot of PCIe, and xptrtrdma is a NFS-RDMA
> workload.

We need to get a better idea what correctness testing has been done,
and whether positive correctness testing results can be replicated
on a variety of platforms.

I have an old Haswell dual-socket system in my lab, but otherwise
I'm not sure I have a platform that would be interesting for such a
test.

> AMD dual socket systems are well known to benefit from relaxed
> ordering, people have been doing this in userspace for a while now
> with the opt in.

--
Chuck Lever