Designing efficient interconnects to support high-bandwidth and
low-latency communication is critical toward realizing high
performance computing (HPC) and data center (DC) systems in the
exascale era. At extreme computing scales, providing the requisite
bandwidth through overprovisioning becomes impractical. These
challenges have motivated studies exploring reconfigurable network
architectures that can adapt to traffic patterns at runtime using
optical circuit switching. Despite the plethora of proposed
architectures, surprisingly little is known about the relative
performances and trade-offs among different reconfigurable network
designs. We aim to bridge this gap by tackling two key issues in
reconfigurable network design. First, we study how cost, power
consumption, network performance, and scalability vary based on
optical circuit switch (OCS) placement in the physical topology.
Specifically, we consider two classes of reconfigurable architectures:
one that places OCSs between top-of-rack (ToR)
switches—ToR-reconfigurable networks (TRNs)—and one that places OCSs
between pods of racks—pod-reconfigurable networks (PRNs). Second, we
tackle the effects of reconfiguration frequency on network
performance. Our results, based on network simulations driven by real
HPC and DC workloads, show that while TRNs are optimized for low
fan-out communication patterns, they are less suited for carrying high
fan-out workloads. PRNs exhibit better overall trade-off, capable of
performing comparably to a fully non-blocking fat tree for low fan-out
workloads, and significantly outperform TRNs for high fan-out
communication patterns.