Parallel Algorithm Design for Workstation Clusters

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SOFTWARE—PRACTICE AND EXPERIENCE, VOL.

Parallel Algorithm 21(3), 235–250 (MARCH 1991)

Design for Workstation

Clusters

J. N. MAGEE AND S. C. CHEUNG

Department of Computing, Imperial College University of London, 180 Queen’s Gate,

London SW7 2BZ, U.K.

SUMMARY

Clusters of workstations connected by local area networks are in common use in many organizations.

The combined processing power of these clusters is rarely exploited owing to the lack of suitable parallel algorithms. The paper describes a parallel programming paradigm called supervisor–worker, suitable

for the workstation environment, which can be used to speed up the execution of a large class of existing

sequential programs. Simple formulae are developed to predict the speed-up of a parallel algorithm developed in this way. The predictions depend on two easily-determined parameters of the sequential program and the characteristic communication cost of the workstation cluster. Consequently, it is possible to estimate the benefits of the parallel program before proceeding with detailed implementation. As an

example, the parallel version of a travelling salesman program is developed and the measured speed-up

compared with the predicted speed-up.

KEY WORDS Parallel algorithm Workstation Travelling salesman Speed-up Distributed system

INTRODUCTION

The availability of high capacity local area networks such as Ethernet has led to the provision of general purpose computing facilities as clusters of workstations which share common resources such as file stores and printers. The benefits of this architec-ture to users over centralized systems (apart from reduced cost) are the provision of a graphic user interface and the predictability of response time which accrues from dedicating a processor to each user. The disadvantage is that the maximum CPU power available to each user on his workstation is generally limited to a lower value than that which would be available on an equivalent centralized system. The user has lost the ability to exploit the entire processing power of an idle central processor for CPU-intensive jobs. This disadvantage can be offset to some extent by a remote job execution facility which allows users to submit work to idle workstations. Recent work has concentrated on scheduling algorithms for allocating background jobs to idle workstations.1 However, this still limits the CPU power available to an individual sequential job. This paper investigates the use of workstation clusters as parallel processors.We concentrate on the development of parallel versions of existing sequential programs to exploit this parallel processing capability of clusters of workstations.