The Wisconsin Wind Tunnel: virtual prototyping of parallel computers

Abstract

We have developed a new technique for evaluating cache coherent, shared-memory computers. The Wis-consin Wind Tunnel (WWT) runs a parallel shared-memory program on a parallel computer (CM-5) and uses execution-driven, distributed, discrete-event simulation to accurately calculate program execution time. WWT is a virtual prototype that exploits sim-ilarities between the system under design (the tar-get) and an existing evaluation platform (the host). The host directly executes all target program instruc-tions and memory references that hit in the target cache. WWT’S shared memory uses the CM-5 mem-ory’s error-correcting code (ECC) as valid bits for a fine-grained extension of shared virtual memory. Only memory references that miss in the target cache trap to W WT, which simulates a cache-coherence protocol. WWT correctly interleaves target machine events and calculates target program execution time. WWT runs on parallel computers with greater speed and memory capacity than uniprocessors. WWT’S simulation time decreases as target system size in-creases for fixed-size problems and holds roughly con-stant as the target system and problem scale.