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Evaluating Network Processing Efficiency with Processor Partitioning and Asynchronous I/O
Brecht, Tim; Janakiraman, G. (John); Lynn, Brian; Saletore, Vikram; Turner, Yoshio
HPL-2005-211R1
Keyword(s): network processing; asynchronous I/O; TCP/IP; multi- core processors
Abstract: Applications requiring high-speed TCP/IP processing can easily saturate a modern server. We and others have previously suggested alleviating this problem in multiprocessor environments by dedicating a subset of the processors to perform network packet processing. The remaining processors perform only application computation, thus eliminating contention between these functions for processor resources. Applications interact with packet processing engines (PPEs) using an asynchronous I/O (AIO) programming interface which bypasses the operating system. A key attraction of this overall approach is that it exploits the architectural trend toward greater thread-level parallelism in future systems based on multi-core processors. In this paper, we conduct a detailed experimental performance analysis comparing this approach to a best-practice configured Linux baseline system. We have built a prototype system implementing this architecture, ETA+AIO (Embedded Transport Acceleration with Asynchronous I/O), and ported a high-performance web-server to the AIO interface. Although the prototype uses modern single-core CPUs instead of future multi-core CPUs, an analysis of its performance can reveal important properties of this approach. Our experiments show that the ETA+AIO prototype has a modest advantage over the baseline Linux system in packet processing efficiency, consuming fewer CPU cycles to sustain the same throughput. This efficiency advantage enables the ETA+AIO prototype to achieve higher peak throughput than the baseline system, but only for workloads where the mix of packet processing and application processing approximately matches the allocation of CPUs in the ETA+AIO system thereby enabling high utilization of all the CPUs. Detailed analysis shows that the efficiency advantage of the ETA+AIO prototype, which uses one PPE CPU, comes from avoiding multiprocessing overheads in packet processing, lower overhead of our AIO interface compared to standard sockets, and reduced cache misses due to processor partitioning.
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