调好学习率,普通LoRA就能打遍天下。
Learning Rate Matters: Vanilla LoRA May Suffice for LLM Fine-tuning
- 系统测试多种LoRA变体,重点调整学习率等超参数。
- 调优后各方法性能差距仅1-2%,表现基本一致。
- 发现学习率差异源于海森矩阵特征值,符合经典理论。
低秩适应(LoRA)是当前主流的大语言模型高效微调方法。近期研究提出了不同的初始化策略、结构修改和优化调整,宣称显著优于原始LoRA。然而这些提升常在固定或窄范围超参数设置下展示,而神经网络对训练配置极为敏感。本文通过大规模超参数搜索(学习率、批量大小、秩、训练时长),系统重评了九种代表性LoRA变体与原始LoRA的表现。在数学推理、常识推理、代码生成和指令遵循等多任务、多模型规模场景下,不同方法偏好不同学习率范围。关键发现:一旦学习率充分调优,所有方法达到相近峰值性能(差异仅1-2%),仅存在细微的秩依赖行为。这表明原始LoRA仍是有力基线,单一配置下的性能提升未必反映方法本身的普适优势。二次分析表明,最优学习率范围的差异源于最大海森矩阵特征值的变化,与经典学习理论一致。
原文摘要 · Abstract (English)
Low-Rank Adaptation (LoRA) is the prevailing approach for efficient large language model (LLM) fine-tuning. Building on this paradigm, recent studies have proposed alternative initialization strategies, architectural modifications, and optimization adjustments, reporting substantial improvements over vanilla LoRA. However, these gains are often demonstrated under fixed or narrowly tuned hyperparameter settings, despite the known sensitivity of neural networks to training configurations. In this work, we systematically re-evaluate nine representative LoRA variants alongside vanilla LoRA through extensive hyperparameter searches over learning rate, batch size, rank, and training duration. Across tasks spanning mathematical reasoning, commonsense reasoning, code generation, and instruction following at diverse model scales, we find that different LoRA methods favor distinct learning rate ranges. Crucially, once learning rates are properly tuned, all methods achieve similar peak performance (within 1-2%), with only subtle rank-dependent behaviors. These results suggest that vanilla LoRA remains a competitive baseline and that improvements reported under a single training configuration may not reflect consistent methodological advantages. Finally, a second-order analysis attributes the differing optimal learning rate ranges to variations in the largest Hessian eigenvalue, aligning with classical learning theories.
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