While constraining the speculation in time warp (TW) tends to decrease the number of false event executions, it also introduces an opportunity cost when the processors are not fully utilized. To obtain good runtime performance such a trade-off must be optimized. This paper studies the implications of regulating speculation in TW, and develops an analytic framework for optimizing the elapsed time of TW simulations. By aggregating the effect of three time components, namely computation time, communication time and processor idle time, our analytic framework optimizes the degree of speculation for AP3000 performance. Our experiments on a Fujitsu AP3000 distributed-memory parallel computer simulating several applications show that the predicted performance metrics deviate from the measured values by less than 8%. Both the analytical and experimental results have ascertained that speculation without rollbacks may not produce the best elapsed time. Instead, a controlled degree of causality error is preferred in most practical cases.
['Seng Chuan Tay', 'Yong Meng Teo']
Performance optimization of throttled time-warp simulation