MLP-Aware Runahead Threads in a Simultaneous Multithreading Processor

Abstract. Threads experiencing long-latency loads on a simultaneous multithreading (SMT) processor may clog shared processor resources without making forward progress, thereby starving other threads and reducing overall system throughput. An elegant solution to the long-latency load problem in SMT processors is to employ runahead execution. Runahead threads do not block commit on a longlatency load but instead execute subsequent instructions in a speculative execution mode to expose memory-level parallelism (MLP) through prefetching. The key benefit of runahead SMT threads is twofold: (i) runahead threads do not clog resources on a long-latency load, and (ii) runahead threads exploit far-distance MLP. This paper proposes MLP-aware runahead threads: runahead execution is only initiated in case there is far-distance MLP to be exploited. By doing so, useless runahead executions are eliminated, thereby reducing the number of speculatively executed instructions (and thus energy consumption...

• Type: Conference
• Year: 2009
• Where: HIPEAC
• Authors: Kenzo Van Craeynest, Stijn Eyerman, Lieven Eeckhout
• Keywords: HIPEAC 2009, Long-latency Load, MLP-aware Runahead Threads, Runahead Threads, System Software