Breaking the Duplex Barrier: Lane-Granularity OCS Scheduling for LLM Training

2026-09-12

AI Summary

本文提出LACE，一种新的OCS调度编译器，通过独立分配发送和接收通道解决大语言模型训练中的不对称通信问题，提高通信速度。

Abstract

Optical circuit switch (OCS) can reconfigure physical connectivity to match the predictable communication schedules of large language model (LLM) training. Although each OCS light path is physically simplex, existing demand-aware OCS schedulers allocate capacity in duplex-port pairs, forcing equal bandwidth in both directions and stranding capacity under asymmetric node-pair traffic. This paper present LACE, the first offline OCS schedule compiler that independently allocates transmit (TX) and receive (RX) lanes for LLM training. Without changing the selected collective algorithms, operation order, or rank placement, LACE reconstructs directed node-level demand, jointly determines which consecutive operations share a configuration and how many simplex circuits serve each direction, and realizes these allocations as physical lane bindings and optical paths under per-node lane-inventory and multi-OCS fabric constraints. Software acknowledgments carry feedback over independently provisioned return paths, while coordinated link configuration and recovery verify each configuration before communication resumes. On a separate three-server testbed using fixed topologies and matched per-port rate limits, LACE's asymmetric connectivity achieves $1.80\times$ speedup for communication replay and $1.27\times$ for GPT-2 training over a symmetric-topology baseline. At larger scale, simulations of LLaMA-3.1 70B and 405B schedules with sixteen 400-Gb/s ports per server show that LACE achieves $1.21$--$2.04\times$ communication speedup over the latest duplex OCS scheduler.

Problem

• Optical Circuit Switch
• OCS Scheduling
• Large Language Model
• Asymmetric Traffic
• Communication Efficiency

Innovation

• OCS Scheduling
• Asymmetric Connectivity
• Large Language Model Training
• Lane-Granularity
• Communication Speedup