Layout-aware expandable low-degree topology

Abstract

System expandability becomes a major concern for highly-parallel computers and datacenters, because their number of nodes gradually increases year by year. In this context we propose a low-degree expandable topology and its floor layout in which a cabinet or node set can be newly inserted by connecting short cables to a single existing cabinet. Our graph analysis shows that the proposed topology has low diameter, low average shortest path length and short aggregate cable length comparable to existing topologies with the same degree. When incrementally adding nodes and cabinets to the proposed topology, its diameter and average shortest path length increase modestly. Flit-level network simulation results show that the proposed topology has lower latency for three synthetic traffic patterns as expected from graph analysis. Our event-driven network simulation results show that the proposed topology provides a comparable performance to 2-D torus even for bandwidth-sensitive parallel applications.