Understanding supercritical speedup

Abstract

Simulations running under Time Warp using lazy cancellation can beat the bound given by the critical path. We explain this phenomenon to be the result of a kind of intra-object parallelism. Specifically, we show that instances of beating the critical path, called supercritical speedup , are made possible by messages that are independent of some event which precedes the message. This insight leads to a new definition for the critical path which is a tighter lower bound on Time-Warp simulations using lazy cancellation than any previously proposed. These results suggest criteria for choosing between lazy and aggressive cancellation.