Dynamic Priority Assignment Scheme for Contract-Based Resource Management

Multimedia execution in high-quality consumer electronics must handle frequent changes in the resource demands of the running applications. These changes can be due to, for instance, a switch in the nature of the incoming media or a user trigger to change the visual focus to a different application. These situations require real-time adaptation mechanisms to adjust the system operation to the new requirements seamlessly. Contract-based resource management allows dealing with these transitions guaranteeing that greedy multimedia applications do not suffer execution interference. A contract model has to be based on efficient resource budget assignment and enforcement to application tasks; this ensures transitioning to the new situation in a stable and safe way but at the cost of having a rigid resource allocation and enforcement to tasks. This paper presents a simple priority reassignment scheme based on uniform priority bands to allow that overrunning tasks execute if they do not threaten timely execution of non-overrunning tasks. It is described how this scheme is integrated with an effective resource accounting and monitoring mechanism; this integration serves as the basic mechanism to support dynamic adaptation in multimedia embedded systems. As proof of concept, this approach has been implemented in a QoS Resource Manager that follows the HOLA-QoS architecture. The experimental results show how multimedia application execution using the simple priority reassignment scheme on top of a resource accounting mechanism preserves timely multimedia delivery.