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arXiv · 2610.03415

RailWave: Adaptive Spatial and Temporal Scheduling for Expert-Parallel Communication

Chutian Wang·Wenhao He·Jingmin Zhu·Qingyu Yin·Heng Xu·Xiuyu Li
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Abstract

Irregular All-to-All communication is a major bottleneck in expert-parallel Mixture-of-Experts (MoE) models. Even with fixed expert routing and placement, uneven utilization of parallel network Rails and incast can limit communication performance. We present RailWave, a phase-adaptive communication layer built on DeepEP that addresses these bottlenecks below the routing layer through spatial and temporal traffic shaping. RailBalance redistributes source traffic across eligible Rails using source-local information, while a reusable, topology-derived permutation schedule limits concurrent senders per receiver without rebuilding demand-dependent schedules for each communication phase. A lightweight calibrated selector chooses an execution path according to each phase's traffic characteristics and offline profiling results. On training-derived communication workloads from the 106B GLM-4.5-Air model, RailWave delivers up to 5.84x speedup on H800 and 4.36x on H20 over Native. Code is available at https://github.com/CyberSecurityErial/RailWave-EP.

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Chutian Wang, Wenhao He, Jingmin Zhu, Qingyu Yin, Heng Xu, Xiuyu Li. 2026-10-02. RailWave: Adaptive Spatial and Temporal Scheduling for Expert-Parallel Communication. https://arxiv.org/abs/2610.03415

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