MFLUSH: handling long-latency loads in SMT on-chip multiprocessors

Abstract

Nowadays, there is a clear trend in industry towards employing the growing amount of transistors on chip in replicating execution cores (CMP), where each core is Simultaneous Multithreading (SMT). State-of-the-art high-performance processors like the IBM POWER5 and POWER6 corroborate this CMP+SMT trend. Within each SMT core any of the well-known SMT mechanisms may be applied to face SMT related challenges. Among them, probably the most important issue in an SMT execution pipeline concerns the In-struction Fetch (IFetch) Policy. The FLUSH IFetch Policy represents a choice for throughput-oriented scenarios. It handles L2 cache misses in order to avoid hardware resource monopolization by any given execution Thread; involving an additional energy cost via instruction refetching. However, the new constraints imposed by the CMP+SMT scenario may a ect wellknown SMT mechanisms, like the FLUSH mechanism.