Controlware: A middleware architecture for feedback control of software performance

Attainment of software performance assurances in open, largely unpredictable environments has recently become an important focus for real-time research. Unlike closed embedded systems, many contemporary distributed real-time applications operate in environments where offered load and available resources suffer considerable random fluctuations, thereby complicating the performance assurance problem. Feedback control theory has recently been identified as a promising analytic foundation for controlling performance of such unpredictable, poorly modeled software systems, the same way other engineering disciplines have used this theory for physical process control. In this paper, we describe the design and implementation of ControlWare, a middleware QoS-control architecture based on control theory, motivated by the needs of performance-assured Internet services. It offers a new type of guarantees we call convergence guarantees that lie between hard and probabilistic guarantees. The efficacy of the architecture in achieving its QoS goals under realistic load conditions is demonstrated in the context of web server and proxy QoS management.