Exploring the Limits of Port Reduction in Centralized Register Files

Register file access falls on the critical path of a microprocessor because large heavily ported register files are used to exploit more parallelism. In this paper, we focus on reducing register file complexity by reducing the number of register file read ports. The goal of this paper is to explore the limits of read port reduction in a centralized integer register file i.e. how few read ports can be provided to a centralized integer register file, while still maintaining performance? A naive port reduction may result in significant performance degradation and does not give a true measure of the limits, while clever techniques may be able to further reduce the number of ports. Hence, in this paper, we drastically reduce the number of ports and then investigate techniques to improve the performance of the reduced-ported register file. Our experiments show that the techniques allow further port reduction by improving the performance from reduced-ported RFs. For instance, with our experimental parameters, the naive port reduction method requires at least five read ports to maintain a performance impact of less than 5%, whereas, our techniques require only three ports.