Multi-level QoS Support with Variable Window Size in Weakly Hard Real-Time Systems

Weakly hard real-time model has been successfully used for scheduling in firm real-time systems where some deadline misses are tolerable. The tolerable deadline misses are specified using a (m, k) tuple, which means that tasks are desired to meet m deadlines in any k consecutive task invocations. This model is adopted to provide QoS in many applications such as control systems or multimedia applications. In this paper, we show that multiple QoS levels can be provided using (m, k) constraint with variable window size k. Even though the size of window k is changed at run time, it is shown that the QoS level with minimum ratio of m/k is guaranteed for evenly distributed pattern. Using this guarantee, we show that higher utilization with equal or higher QoS can be achieved in overload management.