Newsgroups: comp.parallel.mpi
From: Mike Ashworth <ashworth@dkrz.de>
Subject: Re: MPI-Benchmarking
Organization: Deutsches Klimarechenzentrum
Date: Wed, 30 Oct 1996 10:38:17 +0100
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Message-ID: <32772209.2F80@dkrz.de>

Peter Sanders wrote:

> - We are aware of a number of evaluations of communication
>   performance. But so far, few have used MPI, the number of
>   measured functions is relatively small and the
>   measurement code is usually not accessible.

Hi Peter,

We have developed a low-level communications benchmark which you
may like to look at. Called OCCOMM it is designed to measure message
passing performance using a simple message exchange protocol 
for contiguous, single-strided and double-strided data commonly found in
regular grid-based models, e.g. ocean models (hence the name).
It is currently available using MPI, PVM and Cray's SHMEM library
and is designed to test a wide range of functions from these libraries.

For more information and access to code and results from a range of
machines see
http://www.dkrz.de/dkrz/parallel/occomm/home-english.html

Briefly, results show that on modern microprocessor based MPP machines,
such as, but not limited to, the Cray T3D, the speed of inter-processor
communications can exceed the memory-to-memory copy speed. This means
that for communications of non-contiguous data it may be better do
packing of data into contiguous buffer space using optimized code
within the user program rather than using the derived type,
data-in-place or packing facilities of MPI or PVM. Best of all on the
T3D is to forget packing entirely and send using multiple SHMEM_put or
SHMEM_iput calls.

Early results from the Cray T3E show some differences from the T3D but
support the above conclusions.

		Mit freundlichen Gruessen,
			Mike Ashworth.
-- 
                                   ,?,
                                  (o o)
|-----------------------------oOO--(_)--OOo----------------------------|
|                                                                      |
| Dr Mike Ashworth          Deutsches Klimarechenzentrum (DKRZ)        |
| ashworth@dkrz.de          (German Climate Research Computing Centre) |
| Tel: +49 40 41173 395     Bundesstrasse 55, D-20146 Hamburg, Germany |
| Fax: +49 40 41173 270                                                |
| WWW URL: http://www.dkrz.de/dkrz/parallel/parallel-english.html      |
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