A Case for Uni-directional Network Topologies in Large-Scale Clusters
A Case for Uni-directional Network Topologies in Large-Scale Clusters
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DOI：
10.1109/cluster.2017.33
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发表时间：
2017-09
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通讯作者：
M. Koibuchi;Tomohiro Totoki;Hiroki Matsutani;H. Amano;Fabien Chaix;I. Fujiwara;H. Casanova
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作者：
M. Koibuchi;Tomohiro Totoki;Hiroki Matsutani;H. Amano;Fabien Chaix;I. Fujiwara;H. Casanova
设计交换机的低延迟网络拓扑是下一代大规模集群的一个关键目标。低延迟以低跳数为前提，但现有的网络拓扑的跳数比理论下限大得多。为了缓解这个问题，我们提议基于已知跳数接近理论下限的有向图来构建网络拓扑。有向拓扑的一个实际困难是逐交换机的流量控制，我们通过使用热土豆路由（hot - potato routing）解决了这个问题。针对有向拓扑上各种流量模式的精确周期网络模拟实验表明，热土豆路由实现的性能与传统的无死锁路由相当。类似的实验被用于比较几种有向拓扑和双向拓扑，结果表明前者实现了显著更低的延迟和更高的吞吐量。我们通过离散事件模拟量化了并行应用基准测试的端到端应用性能，表明有向拓扑相比双向拓扑能大幅提高应用性能。最后，我们讨论了有向拓扑的一些实际问题，比如布线复杂性和成本、功耗以及软错误容忍度。我们的结果为在即将到来的大规模集群中考虑有向拓扑提供了有力的依据。
Designing low-latency network topologies of switches is a key objective for next-generation large-scale clusters. Low latency is preconditioned on low hop counts, but existing network topologies have hop counts much larger than theoretical lower bounds. To alleviate this problem, we propose building network topologies based on uni-directional graphs that are known to have hop counts close to theoretical lower bounds. A practical difficulty with uni-directional topologies is switch-by-switch flow control, which we resolve by using hot-potato routing. Cycle-accurate network simulation experiments for various traffic patterns on uni-directional topologies show that hot-potato routing achieves performance comparable to that of conventional deadlock-free routing. Similar experiments are used to compare several uni-directional topologies to bi-directional topologies, showing that the former achieve significantly lower latency and higher throughput. We quantify end-to-end application performance for parallel application benchmarks via discrete-even simulation, showing that uni-directional topologies can lead to large application performance improvements over their bi-directional counterparts. Finally, we discuss practical issues for uni-directional topologies such as cabling complexity and cost, power consumption, and soft-error tolerance. Our results make a compelling case for considering uni-directional topologies for upcoming large-scale clusters.