Table-based QoS control for embedded real-time systems

This paper proposes a new QoS control scheme that is suited for embedded real-time systems. Our scheme focused on real-time systems where both device control and multimedia processing are required. Such systems needs to keep timing constraints of control tasks while providing the highest possible quality of service(QoS) to multimedia processing tasks. Although many QoS control schemes are proposed and used in distributed multimedia systems, they are not suited for such real-time systems. Their QoS control policies cannot exactly keep the timing constraints of control tasks.To overcome this problem we chose a scheme which uses a table describing resource requirements of all tasks. Resource allocations for tasks and total resource utilization in a system can be calculated from the table. Using our scheme, any QoS control policies, such as a fair-share policy or a priority based policy, can be implemented. In other words, it has become possible for the first time to allow the intention of system designers to be directly reflected on QoS control.We have implemented a CPU time QoS control mechanism based on our proposed scheme and evaluated it on a μ-ITRON Ver. 3.0 based real-time OS. The evaluation results demonstrate that the QoS control scheme can keep deadline misses low and CPU utilization high under an overloaded state. The results also show that overhead of the QoS control mechanism is small enough to support both multimedia and control applications.