Speculative parallel simulation with an adaptive throttle scheme

Abstract

Excessive rollback recoveries due to overoptimistic event execution in Time Warp simulators often degrade their runtime performance. This paper presents a two-sided throttling scheme to dynamically adjust the event execution speed of Time Warp simulators. The proposed throttle is based on a new concept called global progress window, which allows the individual simulation process to be positioned on a global time scale, thereby to accelerate or suspend their event execution. As each simulation process can be throttled to a steady state, excessive rollback recoveries due to causality errors can be avoided. To quantify the effect of rollbacks and for purpose of comparing different Time Warp implementations, we propose two new measures called RPE (number of Rollback events Per committed Event), and ε (relative Effectiveness in reducing rollback overhead). Our implementation results show that the proposed throttle effectively regulates the proceeding of each simulation process, resulting in a significant reduction in rollback thrashing and elapsed time.