Interactive debugging and performance analysis of massively parallel applications

In the field of high performance computing, massively parallel processing systems (MPPs) get more and more important. A rising number of complex applications is parallelized for execution on these machines. Still a significant portion of the time needed for parallelization is spent for the process of debugging and performance tuning. A main reason for this fact is the absence of adequate tools supporting this phase of program development. In this article, we present a novel tool environment, consisting of a parallel debugger (DETOP), a performance analyzer (PATOP), and a common monitoring system for PowerPC-based parallel computers. The environment specifically addresses the topics of scalability, usability for dynamic, multithreaded programming models, minimal intrusion, debugging and tuning methodology and comfortable user interfaces. We derive requirements for tools monitoring the runtime behavior of parallel programs, present the concepts used to meet these requirements in our tool environment, and describe its implementation and its usage. DETOP is based on the event-action paradigm and supports both data parallel codes and programs based on functional decomposition. Special features are provided for applications that dynamically create new threads or consist of multiple executables. PATOP supports a systematic search for performance bottlenecks in massively parallel applications using the concept of attributed measurements and distributed evaluation. Both tools are based on a common, distributed on-line monitoring system providing the necessary runtime information.