VCS: A method of in-order packet delivery for adaptive NoC routing

摘要

Adaptive routing proves its efficiency in sustaining higher network performance bypassing packetsthrough alternate congestion-free minimal or non-minimal routes for a many-core on-chip communicationsystem. It prevents the network from reaching an early saturation due to the stalling of packetsin the priority-fixed shortest route for a longer period. However, routing packets adaptively to analternate route instead of choosing the priority-fixed and shortest route may lead to an unintendedstate of delivering packets out-of-order sequence at the destination node that is not accepted by manymessage-passing systems. This ordering mismatch is due to allowing multiple alternate routes forpackets of the same communication flow in adaptive mode. In such a case, a packet with a highersequence number takes over another packet of the same communication flow having a lower sequencenumber. Storing and reordering all unordered packets of the same communication flow at the sink sidebecomes costlier due to the increasing area and power requirement. Ideally, the added memory sizereaches to infinity for storing all unordered packets that belong to the same communication flow. Inthe proposed method, we guarantee delivery of all packets belongs to the same communication flowin an orderly manner under adaptive routing mode. In particular, we have proposed a flow-controlpolicy based on a virtual circuit switch (VCS) method that exclusively won and reserve a virtual path forrouting packets in an adaptive mode for each communication flow. To maximize network performance,we allow sharing of the reserved path among packets of different communication flows, routing underpriority fix deterministic mode. The method saves need of having additional memory unit for storingall unordered packets while guaranteeing the packet’s ordering sequence at the destination end. Anexperiment conducted on two different size Mesh networks (8x8 and 12x12) under several synthetictraffic and benchmark application reveals that our virtual circuit switching (VCS) based proposedmethod offers a significant improvement over the state-of-the-art packet reordering method (ROR)and two similar type of research works. Our simulation based experimental result shows that methodoffers a 60 higher saturation point and 21 improvements (maximum) in throughput while offeringa reduction of 60 in NoC area and 58 power value compared to the baseline reorder (ROR) method.