Exploring configurations of functional units in an out-of-order superscalar processor

This study has been carried out in order to determine cost-effective configurations of functional units for multiple-issue out-of-order superscalar processors. The trace-driven simulations were performed on the six integer and the fourteen floating-point programs from the SPEC 92 suite. We first evaluate the number of instructions allowed to be concurrently processed by the execution stages of the pipeline. We then apply some restrictions on the execution issue of different instruction classes in order to define these configurations. We conclude that five to nine functional units are necessary to exploit Instruction-Level Parallelism. An important point is that several data cache ports are required in a processor of degree 4 or more. Finally, we report on complementary results on the utilization rate of the functional units.