Extracting Critical Path Graphs from MPI Applications

Martin Schulz

IEEE International Conference on Cluster Computing (Cluster 2005)
Boston, Massachusetts, USA, September 27 - 30, 2005

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Abstract

The critical path is one of the fundamental runtime characteristics of a parallel program. It identifies the longest execution sequence without wait delays throughout the code. In other words, the critical path is the global execution path that inflict wait operations on other nodes without itself being stalled. Hence, the critical path dictates the overall runtime and knowing it is important to understand an application's runtime and message behavior and to target optimizations.

We have developed a toolset that identifies the critical path of MPI applications, extracts it, and then produces a graphical representation of the corresponding program execution graph to visualize it. To implement this, we intercept all MPI library calls, use the information to build the relevant subset of the execution graph, and then extract the critical path from there. We have applied our technique to several scientific benchmarks and successfully produced critical path diagrams for up to 128 processors.

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Maintainer: rrgerber@softconf.com