DescriptionThe OpenFlow-style Software Defined Networking (SDN) technology has shown promising performance in data centers and campus networks; and the HPC community is significantly interested in adopting the SDN technology. However, while OpenFlow-style SDN allows dynamic per-flow resource management using a global network view, it does not support adaptive routing, which is widely used in HPC systems. This gives rise to the question whether SDN can achieve the performance that HPC systems expect with adaptive routing. In this work, we investigate possible methods to apply the SDN technology on the current generation HPC interconnects with the Dragonfly topology, and compare the performance of SDN with that of adaptive routing. Our results indicate that adaptive routing results in higher performance than SDN when both have similar resource allocation for a given traffic condition. However, SDN can use the global network view to compete with adaptive routing by allocating network resources more effectively.