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<p><b>Abstract</b>—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 <it>unbounded priority inversion</it>, 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 real-time 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.</p>
Real-time, wormhole routing, virtual channel, feasibility analysis, pipelined circuit switching.

F. Özgüner and S. Balakrishnan, "A Priority-Driven Flow Control Mechanism for Real-Time Traffic in Multiprocessor Networks," in IEEE Transactions on Parallel & Distributed Systems, vol. 9, no. , pp. 664-678, 1998.
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