Amdahl's Law as an Instrumentation Tool for Building Eecient Parallel Code and Corresponding Author

Using Amdahl's law as an instrumentation guide we illustrate a technique for developing e cient code on Massively Parallel Processor (MPP) performance-class networks to solve nontrivial, high performance scienti c problems. We also show the importance of collective communication within the Message Passing Interface (MPI) paradigm for some applications. Given the popularity of Beowulf-like clusters of workstations our work also indicates the necessity of a scalable high performance network for obtaining e cient performance in parallel code. Using our approach we were able to obtain an e ective speedup (comparison with the best sequential time) of 170 when using 256 of the Cray T3E 900 processing elements (PEs) to solve a carbon, molecular-dynamic problem. We also examine the approach on a very di erent application: a Lanczos eigenvalue solver. 3