Feedback Guided Dynamic Scheduling of Nested Loops

In previous papers ([2], [3], [6]) feedback guided loop scheduling algorithms have been shown to be very effective for certain loop scheduling problems. In particular they perform well for problems that involve a sequential outer loop and a parallel inner loop, and timing information gathered during one execution of the parallel inner loop can be used to inform the scheduling of the subsequent execution of this loop. In this paper we consider the extension of these feedback-guided scheduling algorithms to the more important case of nested parallel loops, again within a sequential outer loop. We describe three alternative ways of scheduling nested loops; two are based on reducing the nested loops to a single loop and applying one-dimensional techniques; the third addresses the multidimensionality of the nested loops directly.