Round Robin Thread Selection Optimization in Multithreaded Processors

Abstract

We propose a variation of round-robin ordering in an multi-threaded pipeline to increase system throughput and resource distribution fairness. We show that using round robin with a typical arbitrary ordering results in inefficient use of shared resources and subsequent thread starvation. To address this but still use a simple round-robin approach, we optimally and dynamically sort the order of the round robin periodically at runtime. We show that with 4-threaded workloads, throughput can be improved by over 9% and harmonic throughput by over 3% by sorting thread order at run time. We experiment with multiple stages of the pipeline and show consistent results throughout several experiments using the SPEC CPU 2006 benchmarks. Furthermore, since the technique is still a simple round robin, the increased performance requires little overhead to implement.