Abstract
We present a parallel simulator --- BigSim --- for predicting
performance of machines with a very large number of processors. The
simulator provides the ability to make performance predictions for
machines such as Blue Gene/L, based on actual execution of real
applications. We present this capability using case-studies of some
application benchmarks. Such a simulator is useful to evaluate the
performance of specific applications on such machines even before
they are built. A sequential simulator may be too slow or
infeasible. However, a parallel simulator faces problems of
causality violations. We describe our scheme based on ideas from
parallel discrete event simulation and utilize inherent determinacy
of many parallel applications. We also explore the techniques for
optimizing such parallel simulations of machines with large number
of processors on existing machines with fewer number of processors.