Evaluating Batching for TCP Offload

Ever increasing demand for performance and scalability in server networking has generated significant interest in offloading TCP processing to network adapters. The benefits of TCP offload result from its potential to reduce performance-limiting operations such as interrupts, cache misses, and I/O bus crossings. Exploiting this potential, however, is not easy. Design choices that improve performance for a given hardware configuration, workload or set of network characteristics can reduce performance under different conditions. We have evaluated a TCP offload prototype’s ability to reduce I/O bus crossings focusing on the impact of batching interactions between the host and adapter. Our analysis reveals that latency and the number of bus crossings are sensitive to some key parameters related to batching. We demonstrate the importance of these parameters to the viability of any TCP off-load design.