Virtual Circuit-Switching Network with Flexible Topology for High-Performance FPGA Cluster

As the performance of high-end FPGAs has increased in recent years, it’s getting more important to construct an FPGA cluster for both improved processing performance and power efficiency in data centers and supercomputers. For higher utilization of FPGA resources for various applications, we require a flexible inter-FPGA network which provides various topologies appropriately to different applications while a conventional direct-connection network (DCN) provides only a fixed topology, such like a 2D torus. In this paper, we propose a virtual circuit-switching network (VCSN) for a large-scale FPGA cluster to have a flexible inter-FPGA network, where communication links connecting FPGAs are virtualized on the top of Ethernet frames. We can easily configure the VCSN topology optimized for the application by modifying the destination MAC addresses registered in a table of a frame encoder. We present its efficient protocol, hardware implementation, demonstration with 100Gbps Ethernet, and performance comparison with a conventional direct-connection network for FPGAs. We show that VCSN has higher but acceptable latency and slightly higher throughput in comparison with DCN, so that numerical simulation running with a ring of FPGAs achieves comparable performance for DCN.