Performance specifications and metrics for adaptive real-time systems

While early research on real-time computing was concerned with guaranteeing avoidance of undesirable effects such as overload and deadline misses, adaptive real-time systems are designed to handle such effects dynamically. Various research efforts have addressed the characterization and improvement of the dynamic behavior of real-time systems. However, to the authors' knowledge, no unified framework exists for designing adaptive, real-time software systems based on specifications of desired dynamic behavior. We propose such a framework based on control theory. Using control theory a designer can (i) specify the desired behavior in terms of a set of performance metrics that can be mapped to a dynamic response of the control system, (ii) establish an underlying control model of the real-time systems, and (iii) design a resource scheduler using feedback control design methods to guarantee runtime satisfaction of the specs. This is in contrast to more ad hoc techniques. We also show that simply using long term average performance metrics is not sufficient in designing controllers. We then develop a new algorithm based on two PID controllers that meet both the transient and steady state performance requirements.