提出非均匀张量并行,降低大模型训练中单卡故障带来的性能损失。
Nonuniform-Tensor-Parallelism: Mitigating GPU failure impact for Scaled-up LLM Training
- 故障时自动降低故障节点的并行度,保持部分计算贡献。
- 0.1%卡故障时可避免近10%吞吐下降,接近零损失。
- 适配大规模集群,适合高可靠训练场景使用。
大模型训练通过数据并行(DP)与模型并行(MP)结合扩展至数千个GPU。高效的关键在于在紧密耦合的GPU子集(称作扩展域)内采用张量并行(TP),扩展域越大性能越好。新数据中心架构使扩展域从8卡提升至72卡,通过NVLink连接。但更大的扩展域也扩大了故障影响范围:单卡故障可能导致整个扩展域的TP执行中断,显著降低整体训练吞吐。当仅0.1%的GPU故障时,高并行度任务的训练吞吐可能下降近10%。为此,我们提出非均匀张量并行(NTP),让发生故障的DP副本以更低的TP度运行,其贡献的吞吐等于仍正常工作的GPU比例。同时设计具备更强电热能力的机架,支持故障后扩展域的功率增强;结合NTP,可使故障副本与其他副本同步,实现大规模训练近乎零吞吐损失。
原文摘要 · Abstract (English)
LLM training is scaled up to 10Ks of GPUs by a mix of data-(DP) and model-parallel (MP) execution. Critical to achieving efficiency is tensor-parallel (TP; a form of MP) execution within tightly-coupled subsets of GPUs, referred to as a scale-up domain, and the larger the scale-up domain the better the performance. New datacenter architectures are emerging with more GPUs able to be tightly-coupled in a scale-up domain, such as moving from 8 GPUs to 72 GPUs connected via NVLink. Unfortunately, larger scale-up domains increase the blast-radius of failures, with a failure of single GPU potentially impacting TP execution on the full scale-up domain, which can degrade overall LLM training throughput dramatically. With as few as 0.1% of GPUs being in a failed state, a high TP-degree job can experience nearly 10% reduction in LLM training throughput. We propose nonuniform-tensor-parallelism (NTP) to mitigate this amplified impact of GPU failures. In NTP, a DP replica that experiences GPU failures operates at a reduced TP degree, contributing throughput equal to the percentage of still-functional GPUs. We also propose a rack-design with improved electrical and thermal capabilities in order to sustain power-boosting of scale-up domains that have experienced failures; combined with NTP, this can allow the DP replica with the reduced TP degree (i.e., with failed GPUs) to keep up with the others, thereby achieving near-zero throughput loss for large-scale LLM training.
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