Operating systems support for the evolution of software: an evaluation using WWW server software

Improving an operating system's support for the evolution of software is vital to the goal of reducing the significant sum spent on adapting existing software to changing user requirements, especially to improve the performance of software. Therefore, we proposed the idea that, by increasing an operating system's abilities to observe the software's execution behavior and to evolve its execution behavior using the observed results, the operating system could adapt existing software to changing user requirements without making any changes to the software. We integrated the above abilities into a CPU scheduling mechanism in an operating system, and we verified the usefulness of our idea using existing software, viz. a World Wide Web (WWW) server. In this case, our scheduling mechanism alters the execution behavior of a WWW server by giving preferential use of the CPU resources to server processes handling HTML file requests. This allows the user's requirement for the enhancement of response time during periods of high demand to be satisfied. In order to determine which processes are server processes handling HTML file requests, we introduced the scheduling parameters SLP (Scheduling of Long-wait Processes) and RW (Run/Wait). In this paper, we describe how we predicted and updated the RW parameter based on the observed execution behavior of a WWW server, and we present an experimental validation of our method.