Actas JP2011 - Universidad de La Laguna

Actas XXII Jornadas de Paralelismo (JP2011) , La Laguna, Tenerife, 7-9 septiembre 2011form or local, while the latter introduces contentionand hotspots that reduce performance, as in complementor butterfly. Due to space limitations, only theresults for three traffic patterns are shown as theycan represent the behaviour observed on the rest.These are uniform, bit-complement and butterfly.Figure 4 shows the throughput and latency of kingnetworks using Knaive compared to those of 2d toriand meshes. It proves that the increased degree ofthe king networks outperforms their baseline counterpartsby more than a factor two. The averagelatency on zero load is reduced according to the averagedistance theoretical values. Packets are 16-phitlong, thus making the latency improvement less obviousin the graphs. Observe that king meshes havesignificantly better performance than 2d tori, bothin throughput and latency.Figure 5 presents an analysis of the different routingtechniques under the three traffic patterns andfor 8 × 8 king tori and meshes. Comparing the resultsof networks with different sizes highlights thatthe throughput per node is halved. This is due to thewell known fact that the number of nodes in squarenetworks grows quadratically with the side while thebisection bandwidth grows linearly.For benign traffic patterns, the best results aregiven by Knaive routing. However in adverse traffic,a sensible decrease in performance is observed,caused by the reduced path diversity. As mentionedin Section III this limitation is overcome by theKmiss routing. In fact this routing yields poor performanceunder benign traffic pattern but very goodunder the adverse ones.Our composite routing algorithm KBugal gives thebest average performance on all traffic patterns. Inthe benign situations the throughput is slightly lessthan Knaive. And under adverse traffic, performanceis similar to the Kmiss routing, being even better insome situations. The results show that KBugal givesbetter performance than its more generic predecessorUGAL. As can be seen, under benign traffic aimprovement of 15% is obtained and between 10%(complement) and 90% (butterfly).V. ConclusionIn this paper we have presented the foundations ofking networks. Their topological properties offer tantalisingpossibilities, positioning them as clear candidatesfor future network-on-chip systems. Noteworthyare king meshes, which have the implementationsimplicity and wire length of a mesh yet better performancethan 2d tori. In addition, we have presenteda series of routing techniques specific for kingnetworks, that are both adaptive and deadlock free,which allow to exploit their topological richness. Afirst performance evaluation of these algorithms undersynthetic traffic has been presented in which theirproperties are highlighted. Further study will be requiredto take full advantage of these novel topologiesthat promise higher throughput, smaller latency,trivial partitioning and high fault-tolerance.AcknowledgmentThis work has been funded by the Spanish Ministryof Education and Science (grant TIN2007-68023-C02-01, Consolider CSD2007-00050) and bythe HiPEAC European Network of Excellence.References[1] J. Kim, W.J. Dally, S. Scott, and D. Abts, “Technologydriven,highly-scalable dragonfly topology,” SIGARCHComput. Archit. News, vol. 36, no. 3, pp. 77–88, 2008.[2] S. Scott, D. Abts, J. Kim, and W.J. Dally, “The blackwidowhigh-radix clos network,” SIGARCH Comput. Archit.News, vol. 34, no. 2, pp. 16–28, 2006.[3] J. Kim, J. Balfour, and W. 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