Connection handoff policies for TCP offload network interfaces

This paper presents three policies for effectively utilizing TCP offload network interfaces that support connection handoff. These policies allow connection handoff to reduce the computation and memory bandwidth requirements for packet processing on the host processor without causing the resource constraints on the network interface to limit overall system performance. First, prioritizing packet processing on the network interface ensures that its TCP processing does not harm performance of the connections on the host operating system. Second, dynamically adapting the number of connections on the network interface to the current load avoids overloading the network interface. Third, the operating system can predict connection lifetimes to select long-lived connections for handoff to better utilize the network interface. The use of the first two policies improves web server throughput by 12--31% over the baseline throughput achieved without offload. The third policy helps improve performance when the network interface can only handle a small number of connections at a time. Furthermore, by using a faster offload processor, offloading can improve server throughput by 33--72%.