A virtual deadline scheduler for window-constrained service guarantees

This paper presents an approach to window-constrained scheduling, that is suitable for multimedia and weakly-hard real-time systems. Our algorithm called virtual deadline scheduling (VDS) attempts to service m out of k job instances by their virtual deadlines, that may be some finite time after the corresponding real-time deadlines. By carefully deriving virtual deadlines, VDS outperforms our earlier dynamic window-constrained scheduling (DWCS) algorithm when servicing jobs with different request periods. Additionally, VDS is able to limit the extent to which a fraction of all job instances are serviced late, while maximizing resource utilization. Simulations show that VDS can provide better window-constrained service guarantees than other related algorithms, while having as good or better delay bounds for all scheduled jobs. Finally, an implementation of VDS in the Linux kernel compares favorably against DWCS for a range of scheduling loads.