Rate-based scheduling policy for QoS flows in networks on chip

Several propositions of NoC architectures claim providing quality of service (QoS) guarantees, which is essential for e.g. real time and multimedia applications. The state-of-art in NoC literature provides QoS at design time, using circuit switching and/or priority-based scheduling. Both methods optimize a given network template to achieve the QoS requirements after traffic generation and network simulation. However, modern SoCs may execute applications not devised at design time, and these may easily have its QoS requirements violated by a previously fixed NoC structure. This paper proposes a method to achieve QoS requirements in NoCs at execution time. The proposed rate-based scheduling policy is employed to determine the priority of each QoS flow being transmitted through the network. The basis of this scheduling method is the difference between the rate required by a given flow and the rate currently used by this flow. This difference corresponds to the flow priority used by the scheduler. Differently from traditional priority-based scheduling, the priority is dynamically adjusted. Preliminary results show the efficiency of the rate-based scheduling to meet QoS requirements, by comparing the proposed scheduling to priority-based scheduling.