TCEP: Traffic Consolidation for Energy-Proportional High-Radix Networks.

High-radix topologies in large-scale networks provide low network diameter and high path diversity, but the idle power from high-speed links results in energy inefficiency, especially at low traffic load. In this work, we exploit the high path diversity and non-minimal adaptive routing in high-radix topologies to consolidate traffic to a smaller number of links to enable more network channels to be power-gated. In particular, we propose TCEP (Traffic Consolidation for Energy-Proportional high-radix networks), a distributed, proactive power management mechanism for large-scale networks that achieves energy-proportionality by proactively power-gating network channels through traffic consolidation. Instead of naively power-gating the least utilized link, TCEP differentiates links with the type of traffic (i.e., minimally vs. non-minimally routed traffic) on them since the performance impact of power-gating on minimal traffic is greater than non-minimal traffic. The performance degradation from the reduced number of channels is minimized by concentrating available links to a small number of routers, instead of distributing them across the network, to maximize path diversity. TCEP introduces a shadow link to quickly reactivate an inactive link and Power-Aware progressive Load-balanced (PAL) routing algorithm that incorporates the link power states in load-balancing the network. Our evaluations show that TCEP achieves significantly higher throughput across various traffic patterns while providing comparable energy savings for real workloads, compared to a prior approach proposed for the flattened butterfly topology.