TCP Offload through Connection Handoff

摘要

This paper presents a connection handoff interface between the operating system and the network interface. Using this interface, the operating system can offload a subset of TCP connections in the system to the network interface, while the remaining connections are processed on the host CPU. Offloading can reduce computation and memory bandwidth requirements for packet processing on the host CPU. However, full TCP offloading may degrade system performance because finite processing and memory resources on the network interface limit the amount of packet processing and the number of connections. Using handoff, the operating system controls the number of offloaded connections in order to fully utilize the network interface without overloading it. Handoff is transparent to the application, and the operating system may choose to offload connections to the network interface or reclaim them from the interface at any time. A prototype system based on the modified FreeBSD operating system shows that handoff reduces the number of instructions and cache misses on the host CPU. As a result, the number of CPU cycles spent processing each packet decreases by 16-84%. Simulation results show handoff can improve web server throughput (SEPCweb99) by 15%, despite short-lived connections.