Effective cluster assignment for modulo scheduling

Clustering is one solution to the demand for wide issue machines and fast clock cycles because it allows for smaller, less ported register files and simpler bypass logic while remaining scaleable. Much of the previous work on scheduling for clustered architectures has focused on acyclic code. While minimizing schedule length of acyclic code is paramount, the primary objective when scheduling cyclic code is to maximize the throughput or steady state performance. This paper investigates a pre-modulo scheduling pass that performs cluster assignment in a way that minimizes performance degradation due to explicit communication required as the loops are split over clusters. The proposed cluster assignment algorithm annotates and adjusts the graph for use by the scheduler so that any traditional modulo scheduling algorithm, having no knowledge of clustering, can produce a valid and efficient schedule for a clustered machine.