Visualization Tool for Development of Communication Algorithms and a Case Study Using the K Computer

Syunji Yazaki, Ryohei Suzuki, Fumiyoshi Shoji, Kenichi Miura, Hiroaki Ishihata
In this paper, we introduce our visualization tool, the Communication Log Viewer (CLV), that assists the development of collective communication algorithms. We also present visualiza-tion results as a case study. CLV visualizes information regarding node events and network statistics in linked multiple views. CLV also has a function for analyzing the results obtained from network simulators and actual machines in the same framework, which is useful when developers repeatedly test their
more » ... s on a simulator and an actual system. For a case study, we visually evaluated two all-to-all algorithms on the full system of the K computer that has 82,944 nodes. As a result, we confirmed that an optimized all-to-all algorithm implemented for the K computer performed better than an all-to-all implemented in Open MPI. We also confirmed that the barrier operation used in the K computer's Message Passing Interface (MPI) functions keep link utilization high. However, there is also a trade-off between the number of barriers and link utilization.