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

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Message-ID: <C2924F03-11C5-4839-A4F3-36872194EEA8@oracle.com>
Date:   Mon, 5 Apr 2021 23:42:31 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     Christoph Hellwig <hch@....de>, Leon Romanovsky <leon@...nel.org>,
        Doug Ledford <dledford@...hat.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Adit Ranadive <aditr@...are.com>,
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Subject: Re: [PATCH rdma-next 00/10] Enable relaxed ordering for ULPs



> On Apr 5, 2021, at 4:07 PM, Jason Gunthorpe <jgg@...dia.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@...dia.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