Modeling Ugal On The Dragonfly Topology

The Dragonfly topology has been proposed and deployed as the interconnection network topology for next-generation supercomputers. Practical routing algorithms developed for Dragonfly are based on a routing scheme called Universal Globally Adaptive Load-balanced routing with Global information (UGAL-G). While UGAL-G and UGALbased practical routing schemes have been extensively studied, all existing results are based on simulation or measurement. There is no theoretical understanding of how the UGAL-based routing schemes achieve their performance on a particular network configuration as well as what the routing schemes optimize for. In this work, we develop and validate throughput models for UGAL-G on the Dragonfly topology and identify a robust model that is both accurate and efficient across many Dragonfly variations. Given a traffic pattern, the proposed models estimate the aggregate throughput for the pattern accurately and effectively. Our results not only provide a mechanism to predict the communication performance for large scale Dragonfly networks but also reveal the inner working of UGAL-G, which furthers our understanding of UGAL-based routing on Dragonfly.