Special Purpose Computers

287 Pages·1988·17.097 MB·English

by  Berni J. Alder

Special Purpose Computers
Edited by
BERNI J. ALDER
Lawrence Livermore National Laboratory
Livermore, California
ACADEMIC PRESS, INC.
Harcourt Brace Jovanovich, Publishers
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Copyright © 1988 by Academic Press, Inc.
All rights reserved.
No part of this publication may be reproduced or
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United Kingdom Edition published by
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Library of Congress Cataloging-in-Publication Data
Special purpose computers / edited by Berni J. Alder,
p. cm.—(Computational techniques : v. 5)
Bibliography: p.
Includes index.
ISBN 0-12-049260-1
1. Electronic digital computers. I. Alder, B. J. II. Series.
QA76.5.S6588 1988 87-28914
004—dcl9 CIP
Printed in the United States of America
88 89 90 91 9 8 7 6 5 4 3 2 1
Contributors
Numbers in parentheses refer to the pages on which the authors' contributions begin.
A. F. Bakker (183), University of Technology, Laboratory of Applied Phys-
ics, Lorentzweg 1, 2628 CJ Delft, The Netherlands
H. W. J. Blöte (233), University of Technology, Laboratory of Applied
Physics, Lorentzweg 1, 2628 CJ Delft, The Netherlands
C. Bruin (183), University of Technology, Laboratory of Applied Physics,
Lorentzweg 1, 2628 C J Delft, The Netherlands
E. Clementi (135), IBM Corporation, Data Systems Division, Department
48 B, MS 428, PO Box 100, Neighborhood Road, Kingston, New York
12401
A. Compagner (233), University of Technology, Laboratory of Applied
Physics, Lorentzweg 1, 2628 CJ Delft, The Netherlands
Daniel Dewey (67), Department of Mechanical Engineering, Massachu-
setts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Mas-
sachusetts 02139
William Flannery (97), School of Engineering and Applied Science, Depart-
ment of Mechanical and Aerospace Engineering, D 323, Princeton Univer-
sity, Princeton, New Jersey 08544
vii
viii Contributors
Geoffrey C. Fox (1), Concurrent Computing Group, Mail Code 0 15-79,
California Institute of Technology, Pasadena, California 91125
Ehtesham Hayder (97), School of Engineering and Applied Science, De-
partment of Mechanical and Aerospace Engineering, D 323, Princeton
University, Princeton, New Jersey 08544
A. Hoogland (233), University of Technology, Laboratory of Applied Phys-
ics, Lorentzweg 1, 2628 C J Delft, The Netherlands
D. Logan (135), IBM Corporation, Data Systems Division, Department 48
B, MS 428, PO Box 100, Neighborhood Road, Kingston, New York 12401
D. Nosenchuck (97), School of Engineering and Applied Science, Depart-
ment of Mechanical and Aerospace Engineering, D 323, Princeton Univer-
sity, Princeton, New Jersey 08544
Anthony Patera (67), Department of Mechanical Engineering, Massachu-
setts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Mas-
sachusetts 02139
Anthony E. Terrano (41 ), Department of Electrical and Computer Engi-
neering, School of Engineering, Rutgers University, Piscataway, New Jer-
sey 08854
Introduction
General purpose computers are designed to run a large variety of appli-
cation programs. Since different problems make different demands on a
computer, compromises are made in the design that will limit the effi-
ciency of running any individual program. In contrast, if the computer is
specifically designed to solve a particular problem, every feature of this
computer can be tuned to the problem at hand. For this reason, problems
can be solved orders of magnitude faster on special purpose computers.
The purpose of this book is to describe such computers, which were
especially designed and built to solve particular scientific problems and to
compare them to general purpose computers, in both speed and cost. This
is for the benefit of others who might contemplate similar endeavors.
Drawbacks to the special purpose computer approach are that the de-
signing and building of such computers is more expensive and time con-
suming than developing programs for general purpose computers. More-
over, special purpose computers can rarely be adapted to solve other
problems or be modified to exploit algorithmic improvements. Hence, it is
not advisable to freeze a particular numerical approach into hardware
unless the algorithm is both planned to be used for a long time and also
well established, since as much efficiency can be gained by searching for
better numerical techniques as by better arrangement of the computer
components.
There are many scientific problems that are inherently too complex to
be solved on any general purpose computer available in the foreseeable
future. One such case described in this book is the lattice gauge calculation.
Since the very foundation of high energy physics depends on a numerical
validation of these equations, several special purpose computers have been
ix
χ Introduction
built for solving that problem. One such special purpose computer (the
hypercube) interestingly enough has turned out to be useful for a variety of
other scientific applications. This is a good example of how the building of
a special purpose computer with a different architecture stimulated the
design of a new class of more general purpose computers. On the other
hand, some new computer architectures are built without specific purposes
in mind, although they turn out to be particularly suitable for solving
certain classes of problems. One such example is the connection machine
that solves Ising, cellular automata, and neural networks problems very
efficiently.
The computers that were designed for the efficient solution of long
established algorithms described in this book are Navier-Stokes hydrody-
namic solvers, classical molecular dynamic machines, and Ising model
computers. The hope is that the documentation of the experiences of
building those devices will advance the process of numerically solving
scientific problems.
—Berni J. Alder
Series Editor
1 The Hypercube and the
Caltech Concurrent
Computation Program:
A Microcosm of Parallel
Computing
GEOFFREY C. FOX*
California Institute of Technology
Pasadena, California
I. Original Motivation and Historical
Overview
The CalTech Concurrent Computation Program. An
evolution from computational high energy physics to a
supercomputer initiative.
A. Introduction
This article is a personal impression of the research of the Caltech Concur-
rent Computation Program. Its autobiographical slant allows me to paint
issues as black and white that when averaged over others' outlooks would
t Research supported by the Department of Energy grant, DE-FG03-85ER25009, the Par-
sons Foundation, the Systems Development Foundation, and the office of the program
manager of the Joint Tactical Fusion Office.
Special Purpose Computers 1 Copyright © 1988 by Academic Press, Inc.
All rights of reproduction in any form reserved.
ISBN 0-12-049260-1
2 Geoffrey C. Fox
be muddied and unclear. I should note that I am very grateful to my many
collaborators, but they should not be held responsible for opinions ex-
pressed here; these opinions are my own. We will chronicle the progress of
our research with the purpose of clarifying the lessons learned—from
detailed computer architecture issues to such global points as the trade-offs
between inhouse and commercial development.
The progress of the Caltech Concurrent Computation Program can be
divided into four stages. Birth and early struggles to survive occupied
1981-1983. Carefree youth and unblemished success lasted from
mid-1983 to the end of 1984. Middle age with difficult bittersweet choices
was successfully weathered in 1985 and 1986. In the current stage, we look
to fresh beginnings with new initiatives starting in 1986 and 1987. We give
an overview of these four stages in the remainder of this section.
In Sections II and IV respectively, we describe two particular areas—
hardware and software—where our project, like others, has had successes
but also difficulties. In each case, we discuss the plusses and minuses of
inhouse versus commercial development. We break up these logistic sec-
tions by a description in Section III of the major result of our research —
namely, that a hypercube can be a general purpose supercomputer—and
of how we were led to this conclusion. In the final section, we turn to the
future, where we see a growing interest not in showing that particular
parallel machines are usable but in comparing and evaluating the different
architectures.
This paper is, of course, not complete. We refer to our last annual report
[ 1 ] for a programmatic description of our research. Another subjective and
historical account will be found in [2] which covers more issues but in less
depth.
B. The Beginning
We can trace the origins of our research to the work, led by Chris Cole and
Stephen Wolfram, in developing the Symbolic Manipulation Program
(SMP). This work required us to bring up UNIX on our new VAX11/780,
the first time this had been done at Caltech. This endeavor established our
first ties with the Caltech Computer Science department and I can still
remember Carver Mead urging us to get back with them if we had insolu-
ble large-scale computational needs. However, these events just provided
the ambiance; the real conception of C 3P, the Caltech Concurrent Com-
putation Program, occurred in May 1981 when Carver Mead gave a Phys-
ics Colloquium on VLSI, very large scale integration, and the opportunities
it opened up. By that time, I had switched my interest from symbolic to
numerical computation techniques for QCD, Quantum Chromodynamics.
It had become apparent that (symbolic) evaluation of perturbation series
The Hypercube 3
for QCD missed the point, and only approaches that included nonpertur-
bative effects would allow realistic predictions for a range of observables.
Thus, my approach had changed from SMP to numerical computations
which ran for many days (weeks) on the long-suffering VAX. At Carver's
colloquium, I realized that our QCD calculations could be performed
concurrently and that his VLSI revolution would lead to cost-effective
concurrent computers for this problem.
During the summer of 1981, my research group, especially Eugene
Brooks and Steve Otto, showed that effective concurrent algorithms could
be developed, and we presented our conclusion to the Caltech Computer
Scientists. This presentation led to the plans, described in more detail in
Section II, to produce the first hypercube, with Chuck Seitz and his student
Erik DeBenedictis developing the hardware and my group the QCD soft-
ware. My group did not understand what a hypercube was at that stage, but
agreed with the computer scientists because the planned six-dimensional
hypercube was isomorphic to a 4 X 4 X 4 three-dimensional mesh, a to-
pology whose relevance a physicist could appreciate. With the generous
help of the computer scientists, we gradually came to understand the
hypercube topology with its general advantage (maximum distance be-
tween nodes is log N) and its specific feature of including a rich variety of
2
mesh topologies. Here Ν is the total number of nodes in the concurrent
computer. We should emphasize that our understanding of the relevance
of concurrency to QCD was not particularly novel; it followed from ideas
already known from earlier concurrent machines such as the Illiac IV. We
were, however, fortunate to investigate the issues at a time when micropro-
cessor technology (in particular the INTEL 8086/8087) allowed one to
build large (in terms of number of nodes) cost-effective concurrent com-
puters with interesting performance levels. The QCD problem was also
important in helping ensure that the initial Cosmic Cube was built with
sensible design choices; we were fortunate that in choosing parameters,
such as memory size, appropriate for QCD, we also realized a machine of
general capability.
From the start, we realized that the Cosmic Cube was too small and that
we needed a much larger system for decisive QCD calculations. My initial
attempts to raise money to support this were certainly naive, but I was
fortunate that my conversations with potential funding agencies, especially
Don Austin at DOE and Charles Smith at Systems Development Founda-
tions, forced me to understand the issues more deeply and to develop some
ideas that were perhaps novel. These developed during 1982 while we used
a small four-node test system to develop our QCD applications. I used this
time to explore other applications of the Cosmic Cube as I wandered
around first Campus and then JPL (the Jet Propulsion Laboratory) and
tried to understand the "reason" why many groups were dissatisfied with
4 Geoffrey C. Fox
VAX-class computing and needed more computational power. This led to
one major qualitative discovery: namely, the Cosmic Cube seemed suitable
for many other applications besides its original high-energy physics and
computer science motivation. I was also able to develop a rather quantita-
tive speedup analysis which was later borne out experimentally and is
described in Section III. In early 1983, we put together our first significant
proposals to INTEL, DOE, and the Parsons and Systems Development
Foundations. This started the next phase of the project, since we were
funded to investigate the hypercube as a relatively general-purpose com-
puter for scientific and engineering problems.
C. Carefree Youth
In August 1983, or in reality in the fall quarter of 1983-84, we started our
next phase. The late spring and summer had been full of worry. Would we
get funded? Could we make commitments to key people like my graduat-
ing student S. Otto? Would the Cosmic Cube be finished in a timely
fashion and would it run reliably? How should one organize such a com-
plicated cross-disciplinary project?
In fact, all the issues were answered satisfactorily, and the year or so
beginning in August 1983 was in retrospect the most enjoyable period of
our project. The project was still relatively small and we made some
interesting discoveries that were well received by our peers. The term C 3P
was coined at this time and the initial collaboration included C. Seitz
(computer science), myself (high-energy physics), R. Clayton and B. Hager
(geophysics), A. Kuppermann (chemistry) and H. Keller and P. Saffman
(applied mathematics). We also involved the Jet Propulsion Laboratory at
this stage as a professional engineering team to construct our future hyper-
cube hardware and software.
Our major achievement during 1984 was, I believe, to experimentally
verify the basic assertion of our proposals: yes, the hypercube is a generally
usable concurrent computer. We ran the initial Cosmic Cube for 2500
hours on a QCD calculation of the qq potential; this was at the time better
than the competitive CRAY and CDC-205 calculations. Further, we were
able to develop 10 programs that actually ran on the hypercube and
"solved real problems with real hardware using real software"—still the
underlying motif of our research. These programs also verified the simple
speedup model that I had developed earlier and this success allowed one to
extrapolate their performance to larger systems.
These 10 initial applications are recorded for posterity in [3], an internal
document which we should have published as a collection of papers.
Mistakenly, we decided to write a book, a good but time-consuming idea