Profiling and reducing processing overheads in TCP/IP

This paper presents detailed measurements of processing overheads for the Ultrix 4.2a implementation of TCP/IP network software running on a DECstation 5000/200. The performance results were used to uncover throughput and latency bottlenecks. We present a scheme for improving throughput when sending large messages by avoiding most checksum computations in a relatively safe manner. We also show that for the implementation we studied, reducing latency (when sending small messages) is a more difficult problem because processing overheads are spread over many operations; gaining a significant savings would require the optimization of many different mechanisms. This is especially important because, when processing a realistic workload, we have found that nondata-touching operations consume more time in aggregate than data-touching operations.