[ofa-general] SDP - How to?

[Zafar Gilani]

Yes of course good question. Well the reason is that SDP allows two
approaches: BCopy (Buffered Copy) and ZCopy (Zero Copy or RDMA). BCopy as I
described is simple to use (change AF_INET to AF_INET_SDP in socket() call
and you are done, no code changes). Whereas ZCopy exploits the RDMA
capability of InfiniBand. In contrast IPoIB just provides IP protocol
encapsulation over InfiniBand.

You can look at the benchmark graphs I generated at [
http://hpc.niit.edu.pk/~zafar/work/results_rocks/index.html] by executing
MPJ Express over IPoIB and SDP/BCopy. Now I want to implement SDP/ZCopy for
MPJ Express and I do not know how to do this. This is the primary reason for
my questions :). You can say this is sort of enabling MPJ Express to work
over wide range of IB protocols.

More information on MPJ Express is available at: http://mpj-express.org/

Thank you,
Zafar

On Wed, Jun 10, 2009 at 4:07 PM, Zafar Gilani<zafargilani at gmail.com> wrote:
> I read a paper on "Zero Copy Sockets Direct Protocol over InfiniBand". I
had
> a few questions, if anybody could answer I will be thankful.
>
> 1. SDP BCopy approach can be used without the change of the code via the
use
> of AF_INET_SDP parameter when calling socket() system call. But how can I
> implement SDP ZCopy approach if I want to implement ZCopy_Read and
> ZCopy_Write methods?
>
> 2. Is there any documentation regarding how to implement SDP ZCopy? Any
> Hello World sort of example code that I can use to learn how to work with
> this?
>
> 3. SDP BCopy is better for smaller messages, but how small? Is 64K a good
> threshold to change from BCopy to ZCopy at 128K?

May I ask you why you are looking at SDP ? The performance of IPoIB in
connected mode and with large MTU is close to that of SDP, while the
former is a lot easier to use than the latter.

Bart.
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