Optimal Scheduling of Task Graphs on Parallel Systems

Scheduling tasks onto the processors of a parallel system is a crucial part of program parallelisation. Due to the NP-hard nature of the task scheduling problem, scheduling algorithms are based on heuristics that try to produce good rather than optimal schedules. Nevertheless, in certain situations it is desirable to have optimal schedules, for example for time critical systems or to evaluate scheduling heuristics. This paper investigates the task scheduling problem using A* search algorithm. The A* scheduling algorithm implemented can produce optimal schedules in reasonable time for small to medium sized task graphs. In comparison to a previous approach, the here presented A* scheduling algorithm has a significantly reduced search space due to a much improved cost function f(s) and additional pruning techniques. Last but not least, the experimental results show that the proposed A* scheduling algorithm significantly outperforms the previous approach.