Constraint Analysis and Heuristic Scheduling Methods

Scheduling is one of the main problems that need to be solved by high-level hardware and software compilers. Existing heuristics are often incapable of finding feasible solutions for practical examples, because the tight time and resource constraints make the feasible-solution subspace very small compared to the size of the full search space. For that reason, constraint-analysis techniques that help the scheduler find feasible solutions are nowadays a subject of research. In this paper, the effect of constraint analysis on heuristic schedulers is experimentally quantified to investigate to which extent constraint analysis improves the quality of such schedulers, and also to see which heuristics complement it well. The results show that, for most experiments, constraint analysis helps to improve the obtained schedules in terms of the latency of the schedule. It combines particularly well with the freeing-count heuristic. Keywords—high-level synthesis; scheduling; heuristics; constraint analysis; topological permutation scheduling