Debugging a Parallel Program: Capturing Inter-Processor Communication in an iWarp Torus

To understand or improve the execution behavior of a program on a parallel system, it is often necessary to consider the interaction between the processors in the system. Since communication is important for all parallel programs, obtaining information about the inter-process communication of the program is an important aspect of understanding program execution. If the user's concern is the performance of the parallel program, then the user must be able to capture the dynamic aspects of interprocessor communication. Unfortunately, timing information about inter-processor communication is often not easy to obtain. Building a special-purpose hardware performance monitor is too costly in most scenarios, and the use of VLSI to integrate communication and computation on a single component often provides only a few externally visible measurement points. A software monitor on the other hand is often too slow to allow execution of the monitored program without serious perturbation. Although th..