Dynamic Reconfiguration in Reservation-Based Scheduling: An Optimization Approach

Reservation-based scheduling mechanisms have successfully been used for supporting real-time applications whose tasks exhibit high variability in their execution or release times. Indeed, such mechanisms are able to preallocate system bandwidth to the application tasks so that temporal isolation between them is ensured. However, bandwidth allocation is usually based on off-line policies, which may not be suitable for real-time applications that are structured as having several modes of operation, each one requiring a distinct level of system bandwidth. Variations in light conditions, the changing of energy levels, error-detection, or operator commands are examples of events that may trigger a different mode of operation in multi-mode adaptive real-time applications. In this paper we address the problem of dynamically reconfiguring scheduling parameters of reservation-based mechanisms, offering support for multi-mode adaptive real-time applications. Assuming that each reconfiguration option gives a benefit for the system, reconfiguration is seen as an optimization problem whose objective is to maximize the overall system benefit. Two different models for the problem are formulated, the Integer Programming (IP) and the Linear Programming (LP) formulations. The IP formulation gives rise to an NP-Hard problem for which we give efficient approximate solutions. Also, an optimal and polynomial solution to the LP formulation is derived. Results obtained from extensive simulation indicate the good performance of the proposed reconfiguration mechanisms.