The effectiveness of affinity-based scheduling in multiprocessor networking

Techniques for avoiding the high memory overheads found on many modern shared-memory multiprocessors are of increasing importance in the development of high-performance multiprocessor protocol implementations. One such technique is processor-cache affinity scheduling, which can significantly lower packet latency and substantially increase protocol processing throughput. In this paper, we evaluate several aspects of the effectiveness of affinity-based scheduling in multiprocessor network protocol processing, under packet-level and connection-level parallelization approaches. Specifically, we evaluate the performance of the scheduling technique (1) when a large number of streams are concurrently supported, (2) when processing includes copying of uncached packet data, (3) as applied to send-side protocol processing, and (4) in the presence of stream burstiness and source locality, two well-known properties of network traffic. We find that affinity-based scheduling performs well under these conditions, emphasizing its robustness and general effectiveness in multiprocessor network processing. In addition, we explore a technique which improves the caching behavior and available packet-level concurrency under connection-level parallelism, and find performance improves dramatically