Runahead Threads to Improve SMT Performance

In this paper, we propose Runahead Threads (RaT) as a valuable solution for both reducing resource con-tention and exploiting memory-level parallelism in Si-multaneous Multithreaded (SMT) processors. Our technique converts a resource intensive memory-bound thread to a speculative light thread under long-latency blocking memory operations. These speculative threads prefetch data and instructions with minimal resources, reducing critical resource conflicts between threads. We compare an SMT architecture using RaT to both state-of-the-art static fetch policies and dynamic re-source control policies. In terms of throughput and fairness, our results show that RaT performs better than any other policy. The proposed mechanism im-proves average throughput by 37 % regarding previous static fetch policies and by 28 % compared to previous dynamic resource scheduling mechanisms. RaT also improves fairness by 36 % and 30 % respectively. In ad-dition, the proposed mechanism permits register file size reduction of up to 60 % in a SMT processor without per-formance degradation. 1