Crisis in HPC Discussion - Lyndon J Clarke, Edinburgh Parallel Computing Centre

Newsgroups: uk.org.epsrc.hpc.discussion
From: lyndon@epcc.ed.ac.uk (L J Clarke)
Subject: Re: Crisis-in-HPC conclusions
Organization: Edinburgh Parallel Computing Centre
Date: Wed, 4 Oct 1995 12:59:16 GMT
Message-ID:

IMHO this posting is spot-on. Can we disentangle the performance and software issues in using the parallel machines from the performance and software issues in using the newer faster commodity microprocessors (superscalar, superpipeline, cache, etc)? I do hope so, in fact I believe we must, and from time to time we may not have. These microprocessors appear in parallel machines (esp. MPP type) because these microprocessors appear in workstations.

Yet another 5p worth.

Best Wishes
Lyndon

> This is a point that needs to be repeated and repeated. Sparse matrix problems,
> for instance solving linear systems via conjugate gradients, can completely
> thrash a lot of superscalar superpipelined processors because there is a lot
> of indirect addressing that can cause pipeline stalls and inefficient cache
> utilisation (1 word out of a cache line used etc. etc.).
> 
> A great deal of attention has been paid by developers of numerical software
> to exploit locality of reference and to get reasonable levels of performance
> from a range of processors in an easily configured manner. A lot of this work
> involves fairly significant changes to the underlying algorithms and data
> structures employed. Excellent progress has been made in some problem areas,
> such as solving dense systems of linear equations, and a good deal of new
> generation software with related new algorithms are appearing, but there are
> some big gaps in our ability to exploit a single processor efficiently. 
> 
> I really think much more work needs to be supported in this area, with an
> secondary objective of designing these new algorithms so they can cope with 
> several levels of memory hierarchy and hence have the potential to provide a
> reasonable basis for good parallel software. Developing parallel software and
> tools without addressing this underlying problem is building on a foundation of
> sand -- things are liable to slip from underneath you.
> 

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|e||)| Lyndon J Clarke    Edinburgh Parallel Computing Centre  |  Cymru |
|c||c| Tel: [+ 44] (0)131 650 5021 Email: lyndon@epcc.ed.ac.uk | am Byth|
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