Tuning Parallel Programs with Computational Steering and Controlled Execution

Online visualization and computational steering of parallel scientific applications has been widely recognized as the key to better insight and understanding of the observed simulation. From the parallel program developer's point of view further problems arise and need to be solved. The behavior and performance of parallel programs does not only depend on the input data but also on inter-process communication. To reflect this fact we propose a novel combination of online visualization, computational steering of parallel high performance computing applications and controlled deterministic execution. Both the visualization and the classical part of steering is based on the VIPER tool. For the control of the communication we rely on a tool called codex, which was developed to test and control communication by the use of control patterns. Finally, VIPER and codex form an environment for tuning, steering and testing based on VIPER's extended programming model.