Optimal scheduling of iterative data-flow programs onto multiprocessors with non-negligible interprocessor communication

Abstract

The problem of optimal compile-time multiprocessor scheduling of iterative data-flow programs with feedback (delay elements) is addressed in this paper, unlike the earlier studies assumed the availability of a large number of processors and complete interconnection among them along with the interprocessor communication (IPC) to be non-negligible to be more realistic. We first explain the effects of including IPC in non-overlapped, overlapped, fully-static, and cyclo-static multiprocessor schedules with LMS filter as a realistic example. The effect of IPC in the rate-optimal schedules with the transformation techniques viz. unfolding and retiming in scheduling data-flow programs with optimal unfolding is discussed with an example. We then propose an algorithm, based on the well-known A * algorithm, for optimal scheduling of data-flow programs onto multiprocessors, which uses only minimum number of processors. To alleviate the impediments of large requirements of memory space and CPU time for the optimal scheduling algorithm, we present an effective technique, branch join path isomorphism (BJP) which relies on our previously defined processor isomorphism, task isomorphism, and node isomorphism apart from the lower bound theory and upper bound on the completion time. The schedules produced by our algorithm are superior to those obtained by the earlier algorithms despite considering IPC as non-negligible and also not completely connected multiprocessor systems.