Training large language models (LLMs) with increasingly long and varying sequence lengths introduces severe load imbalance challenges in large-scale data-parallel training. Recent frameworks attempt to mitigate these issues through data reorganization or hybrid parallel strategies. However, they often overlook how computational and communication costs scale with sequence length, resulting in suboptimal performance. We identify three critical challenges: (1) varying computation-to-communication ratios across sequences of different lengths in distributed attention, (2) mismatch between static NIC-GPU affinity and dynamic parallel workloads, and (3) distinct optimal partitioning strategies required for quadratic attention versus linear components.

Efficiently training large language models (LLMs) necessitates the adoption of hybrid parallel methods, integrating multiple communications collectives within distributed partitioned graphs. Overcoming communication bottlenecks is crucial and is often achieved through communication and computation overlaps. However, existing overlap methodologies tend to lean towards either fine-grained kernel fusion or limited operation scheduling, constraining performance optimization in heterogeneous training environments.