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Journal of Inforamtion Science and Engineering, Vol.18 No.2, pp.223-255 (March 2002)

A Release Combined Scheduling Scheme for
Non-Uniform Dependence Loops

Der-Lin Pean, Huey-Ting Chua and Cheng Chen
Department of Computer Science and Information Engineering
National Chaio Tung University
Hsinchu, 300 Taiwan

In general, synchronization mechanisms can be used to preserve dependence constraints in any nested loop, and can be combined with a loop scheduling scheme to form a uniform framework to obtain the correct execution order and balance workload distribution. Most current scheduling mechanisms cannot handle non-uniform dependence loops. In this paper, we propose a new combined scheduling scheme called Release Combined Scheduling for Non-uniform Dependence Loops (RCS) to schedule non-uniform dependence doubly-nested loops in multiprocessor systems. It combines both static and dynamic scheduling mechanisms in order to optimize the system performance. In our approach, initialisation of a set of scheduling information is based on the concept of the minimum dependence distance. During runtime, scheduling information is used to adjust the number of parallelizable iterations. Our method is able to discover more parallelism from a given non-uniform dependence doubly-nested loop than is possible with previous approaches. The experimental results show that the RCS method reliably exploits parallelism and outperforms most of the existing non-uniform dependence loop scheduling schemes by 20.29%, on average.

Keywords: loop scheduling, multiprocessor, non-uniform dependence, hopping gate, hopping distance, synchronization, barrier

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Received April 21, 2000; revised September 1, 2000; accepted December 5, 2000.
Communicated by Chu-Sing Yang.