Software Performance Self-Adaptation through Efficient Model Predictive Control

A key challenge in software systems that are exposed to runtime variabilities, such as workload fluctuations and service degradation, is to continuously meet performance requirements. In this paper we present an approach that allows performance self-adaptation using a system model based on queuing networks (QNs), a well-assessed formalism for software performance engineering. Software engineers can select the adaptation knobs of a QN (routing probabilities, service rates, and concurrency level) and we automatically derive a Model Predictive Control (MPC) formulation suitable to continuously configure the selected knobs and track the desired performance requirements. Previous MPC approaches have two main limitations: i) high computational cost of the optimization, due to nonlinearity of the models; ii) focus on long-run performance metrics only, due to the lack of tractable representations of the QN's time-course evolution. As a consequence, these limitations allow adaptations with coarse time granularities, neglecting the system's transient behavior. Our MPC adaptation strategy is efficient since it is based on mixed integer programming, which uses a compact representation of a QN with ordinary differential equations. An extensive evaluation on an implementation of a load balancer demonstrates the effectiveness of the adaptation and compares it with traditional methods based on probabilistic model checking.