Parallel execution of logic programs by load sharing

Abstract

Execution of a logic program can be sped up by load sharing among a group of interconnected processors. Network contention and load imbalance are two potentially limiting factors that must be dealt with carefully. In this paper, we discuss a task scheduling scheme in which processors share the workload by voluntarily following a universal task distribution rule. Communication is reduced by having processors cooperate without frequent exchange of information. However, load balancing is rendered more difficult. We propose solutions to the problem by altering the shape of a search space to remove the so-called structural imbalance, and by following a statistically even task distribution rule. Simulation and experimental data indicate that the method is effective for a number of programs for which existing scheduling methods tend to generate overly fine-grained tasks that lead to heavy traffic in the network. Speed-up factors by the proposed technique are comparable to, or better than, that by a typical system which relies solely on dynamic task migration to balance the workload. The scheme appears to be particularly suitable for implementation on loosely coupled parallel platforms.