Efficient Queuing Schemes for HoL-Blocking Reduction in Dragonfly Topologies with Minimal-Path Routing

HPC systems are growing in number of connected endnodes, making the network a main issue in their design. In order to interconnect large systems, dragonfly topologies have become very popular in the latest years as they achieve high scalability by exploiting high-radix switches. However, dragonfly high performance may drop severely due to the Head-of-Line (HoL) blocking effect derived from congestion situations. Many techniques have been proposed for dealing with this harmful effect, the most effective ones being those especially designed for a specific topology and a specific routing algorithm. In this paper we present a queuing scheme called Hierarchical Two-Levels Queuing, designed specially to reduce HoL blocking in fully-connected dragonfly networks that use minimal-path routing. This proposal boosts network performance compared with other techniques and requires fewer network resources than the others. Besides, an upgrade for existing queuing schemes for improving their performance is explained.