Design and implementation of a feedback controller for slowdown differentiation on internet servers

Proportional slowdown differentiation (PSD) aims to maintain slowdown ratios between different classes of clients according to their pre-specified differentiation parameters. In this paper, we design a feedback controller to allocate processing rate on Internet servers for PSD. In this approach, the processing rate of a class is adjusted by an integral feedback controller according to the difference between the target slowdown ratio and the achieved one. The initial rate class is estimated based on predicted workload using queueing theory. We implement the feedback controller in an Apache Web server. The experimental results under various environments demonstrate the controller's effectiveness and robustness.