Adaptive TDMA bus Allocation and Elastic Scheduling: a unified approach for enhancing robustness in multi-core RT systems

Next-generation real-time systems will be increasingly based on heterogeneous MPSoC design paradigms, where predictability and performance will be key issues to deal with. Such issues can be tackled both at the hardware level, by embedding technologies such as TDMA busses, and at the OS level, where suitable scheduling techniques can improve performance and reduce energy consumption. Among these, elastic scheduling has been proved to provide satisfactory results by dynamically reducing task periods at run-time to ensure the highest utilization possible of the processors. On the other hand, elastic scheduling lowers the degree of predictability and increases the complexity of the analysis at the system level. This reduces the benefits given by the TDMA bus, which relies on the high level task analysis for a robust and efficient slot allocation. Starting from this consideration, we propose a system where the elastic scheduling and the TDMA bus work synergistically. We introduce a QoS-aware adaptive bus service which takes the best of both techniques, mitigating their drawbacks at the same time. We show how the overhead introduced by coordination action is small, and it is however dominated by the benefits of the overall strategy in terms of performance and predictability guarantees.