Elastic Time

Abstract

We introduce a new class of synchronization protocols for parallel discrete event simulation, those based on near-perfect state information (NPSI). NPSI protocols are adaptive, dynamically controlling the rate at which processes constituting a parallel simulation proceed, with the goal of completing a simulation efficiently. We show by analysis that a class of adaptive protocols (that includes NPSI and several others) can both arbitrarily outperform and be arbitrarily outperformed by the Time Warp synchronization protocol. This mixed result both substantiates the promising results we and other adaptive protocol designers have observed, and cautions those who might assume that any adaptive protocol will always be better than any nonadaptive one. We establish in an experimental study that a particular NPSI protocol, the Elastic Time Algorithm, outperforms Time Warp, both temporally and spatially, on every workload tested. Although significant options remain with respect to the design of ETA, the work presented here establishes the class of NPSI protocols as a very promising approach.