Subject: [nfsv4] Re: [rddp] RE: NFSv4 RDMA and Session Extensions

From: "Talpey, Thomas" <[email-masked]>
Date: Fri, 16 May 2003 20:30:22 -0400

At 04:22 PM 5/16/2003, Caitlin Bestler wrote:
>Section 2.1 (Session Model) includes the following:
>
>> The NFSv4 specification does not provide for any form of
>> flow control;  instead it relies on the windowing
>> provided by TCP to throttle requests.  This unfortunately
>> does not work with RDMA,
>
>I vehemently disagree that this is unfortunate.
>

I agree with your disagreement! :-)

>What is unfortunate is that TCP forced applications to
>confuse the availability of general purpose transport
>buffers with the ability of the server to accept more
>work requests from its clients.
>
>RDMA allows/requires servers to perform ULP flow control
>based upon ULP concepts, such as number of in-flight
>requests.

Yes, and this is the central tenet of our proposal's use of operation
credits to bound the size of the NFS duplicate reply cache, allowing
the server to maintain it on a per-session (i.e. per client) basis and
to enable perfect exactly-once semantics.

So the concept is necessary with RDMA but over TCP the extensions
offer the identical advantage. You might say RDMA teaches an old
dog new tricks!

Thanks,
Tom.

>
>Caitlin Bestler
>http://asomi.com/CaitlinBestler/
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