Re: [nfsv4] Benjamin Kaduk's No Objection on draft-ietf-nfsv4-rpcrdma-cm-pvt-data-07: (with COMMENT)

Tom Talpey <tom@talpey.com> Sun, 01 March 2020 17:24 UTC

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To: Benjamin Kaduk <kaduk@mit.edu>, Chuck Lever <chuck.lever@oracle.com>
Cc: nfsv4-chairs@ietf.org, nfsv4@ietf.org, The IESG <iesg@ietf.org>, draft-ietf-nfsv4-rpcrdma-cm-pvt-data@ietf.org
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From: Tom Talpey <tom@talpey.com>
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Subject: Re: [nfsv4] Benjamin Kaduk's No Objection on draft-ietf-nfsv4-rpcrdma-cm-pvt-data-07: (with COMMENT)
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On 2/20/2020 11:51 AM, Benjamin Kaduk wrote:
> Hi Chuck,
> 
> On Thu, Feb 20, 2020 at 10:13:26AM -0500, Chuck Lever wrote:
>> Hi Ben, thanks for your comments! Responses and questions below.
>>
>>
>>> On Feb 19, 2020, at 8:10 PM, Benjamin Kaduk via Datatracker <noreply@ietf.org> wrote:
>>>
>>> Benjamin Kaduk has entered the following ballot position for
>>> draft-ietf-nfsv4-rpcrdma-cm-pvt-data-07: No Objection
>>>
>>> When responding, please keep the subject line intact and reply to all
>>> email addresses included in the To and CC lines. (Feel free to cut this
>>> introductory paragraph, however.)
>>>
>>>
>>> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
>>> for more information about IESG DISCUSS and COMMENT positions.
>>>
>>>
>>> The document, along with other ballot positions, can be found here:
>>> https://datatracker.ietf.org/doc/draft-ietf-nfsv4-rpcrdma-cm-pvt-data/
>>>
>>>...
>>> Section 6
>>>
>>>    The RPC-over-RDMA version 1 protocol framework depends on the
>>>    semantics of the Reliable Connected (RC) queue pair (QP) type, as
>>>    defined in Section 9.7.7 of [IBA].  The integrity of CM Private Data
>>>
>>> It's interesting to see such a reference to [IBA], when IIUC the RFC
>>> 8166 protocol is not limited to Infiniband as the underlying transport.
>>
>> Correct, RPC/RDMA can operate on iWARP and RoCE as well. However:
>>
>>   - both of those RDMA fabric types also support RC QPs, and
>>   - [IBA] appears to be the only publication where "RC QP type"
>>     is defined, though I could be wrong.
>>
>> I don't read this text as suggesting that RPC/RDMA cannot operate
>> on those alternate fabrics, but perhaps I am "too close to the
>> code".
> 
> I don't read it that way, either; I was just noting that it was surprising
> that this is the only reference available.  If it is, then it is, though,
> so no need to change anything.

The term "RC" or "Reliable Connected" is an InfiniBand-specific term.
The iWARP protocol has neither a datagram nor unreliable mode, therefore
it is an "RC" transport by definition, in InfiniBand-speak.

I do agree that referring normatively to the IB Architecture is odd,
and perhaps unnecessary. Alternatively, the sentence could be relaxed
to avoid this IB-specific term, and describe the situation in an
informative way. "Supports RC-type Infiniband and iWARP Queue Pairs."

There is a document describing the iWARP consumer-visible semantics,
in 2003's https://tools.ietf.org/html/draft-hilland-rddp-verbs-00
However, this document was never adopted as an RDDP work item, and
was not developed further. It is nonetheless an excellent reference
and is frequently referred to.

Tom.