Defining wakeup width for efficient dynamic scheduling

A larger dynamic scheduler (DS) exposes more instruction level parallelism (ILP), giving better performance. However, a larger DS also results in a longer scheduler latency and a slower clock speed. In this paper, we propose a new DS design that reduces the scheduler critical path latency by reducing the wakeup width (defined as the effective number of results used for instruction wakeup). The design is based on the realization that the average number of results per cycle that are immediately required to wake up the dependent instructions is considerably less than the processor issue width. Our designs are evaluated using the simulation of the SPEC 2000 benchmarks and SPICE simulations of the actual issue queue layouts in 0.18 micron process. We found that a significant reduction in scheduler latency, power consumption and area is achieved with less than 2% reduction in the instructions per cycle (IPC) count for the SPEC2K benchmarks.