A priority-driven flow control mechanism for real-time traffic in multiprocessor networks

Real-time applications when mapped to distributed memory multiprocessors produce periodic messages with an associated deadline and priority. Real-time messages may be hard or soft deadline. Real-time extensions to wormhole routing (WR) with multiple virtual channels (VCs) and priority-based physical link arbitration and VC allocation have been proposed in the literature. With a fixed number of VCs/link, a message can face an unbounded priority inversion, rendering the global priority ineffective. In this paper, we propose a new flow control mechanism called Preemptive Pipelined Circuit Switching for Real-Time messages (PPCS-RT) to reduce the priority inversion problem. For the proposed model, with some architectural support, we present an off-line approach to compute delivery guarantees of hard deadline real-time messages. We also perform a comparison of realtime WR and PPCS-RT in terms of performance with soft deadline traffic. The overall miss ratio percentage is over 30 percent higher for WR than PPCS-RT with one VC/link at high traffic loads. Finally, we compare the architectural complexity of a PPCS-RT router and other real-time routers.