Adaptive management of QoS in Open Systems

In this paper, we present a software architecture to support soft real-time applications, such as multimedia streaming and telecommunication systems, in open embedded systems. Examples of such systems are consumer electronic devices (as cellular phones, PDAs, etc.), as well as multimedia servers (video servers, VoIP servers, etc.) and telecommunication infrastructure devices. For such applications, it is important to keep under control the resource utilization of every task, otherwise the Quality of Service experienced by the users may be degraded. Our proposal is to combine a resource reservation scheduler (that allows us to partition the CPU time in a reliable way) and a feedback based mechanism for dynamically adjusting the CPU fraction (bandwidth) allocated to a tasks. In particular, our controller enables specified Quality of Service (QoS) levels for the application while keeping the allocated bandwidth close to its actual needs. The adaptation mechanism consists of the combination of a prediction and of a feedback correction that operates locally on each task. The consistency of the system is preserved by a supervisor component that manages overload conditions and enacts security policies. We implemented the framework in AQuOSA, a software architecture that runs on top of the Linux kernel. We provide extensive experimental validation of our results and offer evaluation of the introduced overhead, which is remarkably lower than the one introduced by other different solutions.