Performance debugging and prediction for parallel systems is a difficult problem. The difficulties in identifying performance bottlenecks stem from the need for an intimate understanding of the underlying architecture. It has been recognized that portability is an important requirement for parallel program development. However, this makes the task of performance debugging even more difficult. In this paper, we present a simulation based approach for performance prediction of portable-parallel programs. We demonstrate it using Charm: a message driven programming environment, which provides program portability across a variety of shared and distributed memory MIMD parallel systems. The proposed approach makes it possible to use a single debugging environment for the development of portable parallel software. This environment can provide correctness and performance debugging support that provides the developer with valuable feedback for improving program performance.