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Vol: 55(69) No: 3 / September 2010

Nature Inspired Metaheuristics for Task Scheduling in Static and Dynamic Computing Environments
Flavia Zamfirache
Department of Computer Science, West University of Timisoara, Faculty of Mathematics and Informatics, Blvd. V. Parvan 4 Timisoara 300223, Romania, phone: (0)256-592155, e-mail: zflavia@info.uvt.ro
Daniela Zaharie
Department of Computer Science, West University of Timisoara, Faculty of Mathematics and Informatics, Blvd. V. Parvan 4 Timisoara 300223, Romania, e-mail: dzaharie@info.uvt.ro
Ciprian Craciun
Department of Computer Science, West University of Timisoara, Faculty of Mathematics and Informatics , Blvd. V. Parvan 4 Timisoara 300223, Romania, e-mail: ccraciun@info.uvt.ro


Keywords: task scheduling, heterogeneous computing environments, evolutionary algorithms, ant colony optimization, dynamic optimization

Abstract
Finding optimal assignments of tasks to processing elements in heterogeneous computing environments is a challenging optimization problem which attracted a lot of researchers during the last decades. The aim of this paper is to analyze the behavior of two nature inspired approaches for task scheduling in static and in dynamic environments.
An evolutionary and an ant based schedulers are proposed. For each one the selection of adequate operators is discussed and some memory based mechanisms are investigated in order to asses their ability to deal with the dynamic nature of the environment. The numerical analysis is based on a well-known benchmark for task scheduling in heterogeneous environments and the dynamic character of the environment is simulated randomly marking some resources as unavailable.
Results obtained by three types of experiments are provided. The first experiment aims to assess the effectiveness of the schedulers in the case of static computing environments. The second experiment is focused on the comparison between the static and dynamic variants of the schedulers tested in the case of the simulated dynamic environment. The last experiment provides results of a robustness analysis.
The numerical results illustrate that the nature inspired schedulers produce good and robust schedules especially in the case of heterogeneous computing environments characterized by inconsistency. In the case of dynamic environments the memory techniques introduced in the nature inspired schedulers proved to be beneficial as long as the ratio of processors which become unaivalable between successive scheduling events is around 10%.

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