Publications

Flexfly: Enabling a Reconfigurable Dragonfly through Silicon Photonics

Wen, Ke; Samadi, Payman; Rumley, Sebastien; Chen, Christine P.; Shen, Yiwen; Bahadori, Meisam; Bergman, Keren; Wilke, Jeremiah J.

The Dragonfly topology provides low-diameter connectivity for high-performance computing with all-to-all global links at the inter-group level. Our traffic matrix characterization of various scientific applications shows consistent mismatch between the imbalanced group-to-group traffic and the uniform global bandwidth allocation of Dragonfly. Though adaptive routing has been proposed to utilize bandwidth of non-minimal paths, increased hops and cross-group interference lower efficiency. This work presents a photonic architecture, Flexfly, which 'trades' global links among groups using low-radix Silicon photonic switches. With transparent optical switching, Flexfly reconfigures the inter-group topology based on traffic pattern, stealing additional direct bandwidth for communication-intensive group pairs. Simulations with applications such as GTC, Nekbone and LULESH show up to 1.8× speedup over Dragonfly paired with UGAL routing, along with halved hop count and latency for cross-group messages. We built a 32-node Flexfly prototype using a Silicon photonic switch connecting four groups and demonstrated 820 ns interconnect reconfiguration time.