Separated High-Bandwidth and Low-Latency Communication in the Cluster Interconnect Clint

Abstract

An interconnect for a high-performance cluster has to be optimized in respect to both high throughput and low latency. To avoid the tradeoff between throughput and latency, the cluster interconnect Clint1 has a segregated architecture that provides two physically separate transmission channels: A bulk channel optimized for high-bandwidth traffic and a quick channel optimized for low-latency traffic. Different scheduling strategies are applied. The bulk channel uses a scheduler that globally allocates time slots on the transmission paths before packets are sent off. This way collisions as well as blockages are avoided. In contrast, the quick channel takes a best-effort approach by sending packets whenever they are available thereby risking collisions and retransmissions. Simulation results clearly show the performance advantages of the segregated architecture. The carefully scheduled bulk channel can be loaded nearly to its full capacity without exhibiting head-of-line blocking that limits many networks while the quick channel provides low-latency communication even in the presence of high-bandwidth traffic.