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原文摘要

Optical circuit-switched networks have emerged as an appealing alternative to electrical fabrics as they can reconfigure the network topology at runtime, reducing communication cost and improving bandwidth utilization. Yet exploiting optical reconfigurable networks for collective communication comes with a fundamental trade-off: each reconfiguration incurs non-negligible delay and the benefit of a new topology depends on future traffic. The central question is therefore when reconfiguration is worth its cost. While prior work has demonstrated the benefits of reconfiguration, the opportunity to reuse optical links to optimize multiple steps remains largely unexplored. In this paper, we present Bridge, a reconfiguration strategy for frequently used collective communication primitives, namely All-to-All, AllReduce, Reduce-Scatter, and AllGather. Bridge exploits the structure of Bruck's communication pattern to support efficient sparse reconfiguration. The key idea is to reduce propagation and transmission delay by directly connecting immediate communication partners and preserve efficient reachability to future peers through connected subrings. As a result, optical links can be reused across multiple subsequent steps, allowing the benefit of reconfiguration to amortize beyond a single step. Our evaluation shows that Bridge reduces All-to-All completion time by typically 3x to 10x over static baselines and is effective even with millisecond-scale reconfiguration delays; for AllReduce up to 1.5x against existing reconfiguration strategies, and by 1.5x to 6.6x against the Ring algorithm on low to moderate-sized workloads.