Effect of state-saving in optimistic simulation on a Cache-Coherent Non-Uniform Memory Access Architecture

Abstract

State-saving and reverse computation are two different approaches by which rollback is realized in Time Warp-based parallel simulation systems. Of the two approaches, state-saving is, in general, more memory-intensive than reverse computation. When executed on a state-of-the-art commercial CC-NUMA (Cache Coherent Non-Uniform Memory Architecture) multiprocessor, our Time Warp system runs almost 6 times slower if state-saving is used than if reverse computation is used. The focus of this paper is to understand why state-saving yields such poor performance when compared to reverse computation on a CC-NUMA multiprocessor. To address this question, we examined the low level machine performance statistics, especially those that relate to memory system performance, such as caching, and translation look-aside buffer (TLB) misses. The outcome of the performance study suggests that TLB misses are the primary culprit for state-saving's performance degradation.