SWiFT : A Feedback Control and Dynamic Reconfiguration

the task of building adaptive system software relies on wizardry. Feedback controls for such software systems are written in an ad-hoc manner and are often brittle. As a result, it is difficult to move an existing control, such as TCP flow control [1], to a new domain such as admission control for CPU scheduling. In addition , existing controls are built with implicit assumptions about the system's run-time environment and can become unstable in the face of large or discontinuous variations in the environment. We advocate a systematic approach for building adap-tive system software based on feedback-control theory. We have implemented the SWiFT toolkit that incorporates this approach. Feedback control helps produce predictable control components. It requires the control goal and design specifications to be clearly stated, thus allowing analysis of properties such as stability. Our approach allows us to leverage the existing body of knowledge in hardware control for controlling software systems. SWiFT allows systematic implementation of feedback control mechanisms by providing a framework and methodology for building controls that are modular, dynamically reconfigurable, and predictable. Modularity results from our use of components and containers as the underlying abstraction. SWiFT also allows easy dynamic reconfiguration of components by limiting the interaction between components to a simple input/output model and by supporting guarding and replugging of controllers [2]. This reconfiguration allows the application to adapt efficiently across a wide range of operating conditions. SWiFT supports predictability by providing analysis tools based on control theory. Also SWiFT provides GUI debugging tools such as a software oscilloscope and a library of feedback components such as low pass filters to simplify building adaptive system software. We have implemented SWiFT in C++ and Java and we have applied it to user-level applications running on Windows NT. Version 1.0 of SWiFT is available (along with a tutorial) at http://www.cse.ogi.edu/DISC/projects/ swift. We are currently building a visual editor for designing , implementing, and monitoring controls using SWiFT. The basic abstractions in SWiFT are feedback components and feedback containers. Feedback components read data from their input port(s), calculate an output value based on their characteristic behavior, and pass the value to their output port. A control circuit is built by connecting a component's output port to input ports of one or more components. A feedback container, provide modularity and hierarchical structure. It is a feedback component that contain other feedback components and containers, and defines a circuit …