Using Libception to Understand and Improve HTTP Streaming Video Server Throughput

Abstract

Video streaming applications generate a large fraction of Internet traffic. Much of this content is delivered over HTTP using standard web servers. Unlike other types of web workloads, HTTP video streaming workloads are typically disk bound, and therefore an important problem is that of optimizing disk access.In this paper we design, implement and evaluate Libception, an application-level shim library that implements techniques for improving disk I/O efficiency. Web servers can achieve the benefits of these techniques simply by linking with Libception, without the need to modify source code. In contrast to making kernel changes or attempting to optimize kernel tuning, Libception provides a portable and relatively simple setting in which techniques for optimizing I/O in HTTP video streaming servers can be implemented and evaluated.We report experimental results evaluating the efficacy of the aggressive prefetching and disk I/O serialization techniques currently implemented in Libception, for three web servers (Apache, nginx and the userver) and two operating systems (FreeBSD, Linux). We find that on FreeBSD, video streaming throughput with all three web servers can be doubled by linking with Libception. On Linux, performance similar to that provided with Libception was eventually obtained by examining the kernel source to understand and tune kernel parameters. With the default kernel parameter settings, however, and regardless of which Linux disk scheduler is selected, we find that use of Libception can approximately double throughput. We find that both aggressive prefetching and serialization are necessary to achieve these benefits.