[Beowulf] Re: Re: Home beowulf - NIC latencies

Patrick Geoffray patrick at myri.com
Wed Feb 16 06:53:43 EST 2005


Hi James,

James Cownie wrote:
> As someone who was on the MPI Forum, and sat through an awful lot of
> meetings, I'd like to provide some justification for _why_ we didn't try
> to make a binary standard.

No, I imagine the context was very different 10 years ago. I just don't 
understand why dynamic spawning, one-sided communications and MPI-IO 
were added to the Standard, but nobody wanted to address the mpi.h 
header compatibility issue. By that time, people knew that it was a 
problem. no ?

 > You seem to think (maybe subconsciously) that the MPI forum added
 > features the standard just to make life hard for implementors and
 > to kill performance ;-)

Well, it was the right thing to be as exhaustive as possible to insure 
the wide adoption of the standard. It was expert friendly, but easy for 
the application folks to miss the points or take shortcuts. That's the 
cose of success.

Now, I would hate to see a shared memory paradigm emerge to 
progressively replace MPI because existing applications don't really try 
to leverage the message passing paradigm capabilities. Some believe it 
will never happen, I am not so sure.

> If you _really_ believe that there is so much performance benefit for
> your customers in having an MPI-light with the restrictions you outlined
> which only runs on your hardware, then no-one's stopping you from
> providing it. 

This discussion is a beginning. It will only happen if all/most MPI 
implementators reach a point where it's clear that to move forward, some 
semantic has to be avoided and some ambiguities cleared, and that can 
only be done at the API level. I would prefer that the MPI forum focus 
on improving the core message passing functionalities instead of adding 
yet another vertical dimension (what's left for MPI-3 ?).

The urgent thing however is the ABI. Can we do that ?

Patrick
-- 

Patrick Geoffray
Myricom, Inc.
http://www.myri.com
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