The impact of packetization in wormhole-routed networks
Packetization is used in a variety of commercial multicomputers because of its potential performance advantages: higher throughput and a better distribution of message latencies. However, packetization has two significant drawbacks, 1) fragmentation and reassembly overhead and 2) increased traffic volume for routing and sequencing information. In this paper, we examine the performance benefits of packetization in existing dimension-order routed networks and in likely future router designs including adaptive routing and virtual lanes.
Our studies show that packetization has a mixed effect on performance in dimension-order routers. Packetizing uniform-sized traffic reduces network throughput dramatically. However, if the traffic is a bimodal distribution of sizes, packetization reduces the variance of latencies for short messages, and increases the network's overall throughput. On the other hand, packetization has no significant impact on the performance of advanced networks with adaptive routing and virtual lanes. Advanced routers without packetization give nearly identical performance to the corresponding packetizing networks under uniform-sized or bimodal traffic. Packetization may be unnecessary in such networks.
KeywordsLatency Distribution Traffic Load Packet Size Average Latency Short Message
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