Distributed Shortcut Networks: Layout-Aware Low-Degree Topologies Exploiting Small-World Effect

Low communication latency becomes a main concern in highly parallel computers and supercomputers. Random network topologies are best to achieve low average shortest path length and low diameter in hop counts between nodes and thus low communication latency. However, random topologies lead to a problem of increased aggregate cable length on a machine room floor. In this context we propose low-degree non-random topologies that exploit the small-world effect, which has been typically well modeled by some random network models. Our main idea is to carefully design a set of various-length shortcuts that keep the diameter small while maintain an economical cable length. Our experimental graph analysis showed that our proposed topology has low diameter and low average shortest path length, which is considerably better than those of a counterpart 2-D torus and is near to those of a counterpart random topology with the same average degree. Meanwhile, the proposed topology has average cable length drastically shorter than that of the counterpart random topology. Our cycle-accurate network simulation results show that the proposed topology has lower latency by 15% and almost the same throughput when compared to torus with the same degree.