对比剪枝与从零训练,发现剪枝在小预算下更优。
Small LLMs: Pruning vs. Training from Scratch

- 在相同训练数据量下,剪枝初始化优于随机初始化。
- 高剪枝率(0.8)时剪枝优势几乎消失,但细粒度剪枝仍胜出。
- 大模型剪枝适合数据有限场景,否则从零训练也可行。
剪枝被视作快速获得高性能小语言模型的捷径。本文通过在六种方法下对 Llama-3.1-8B 进行 0.5–0.8 剪枝率的剪枝,考察该承诺是否成立。在相同训练令牌预算下,剪枝初始化始终优于随机初始化,表明父模型提供强大起点;但随着训练预算增加或剪枝率上升,优势减弱,在最高剪枝率下几乎消失。当从零训练获得完整流水线总训练量时,细粒度剪枝仍具优势,而粗粒度结构化剪枝可被匹配或超越。结果表明:若有大预训练模型且训练预算有限,剪枝更优;若预算充足,粗粒度剪枝下从零训练也具竞争力,大模型并非必需。
原文摘要 · Abstract (English)
Pruning promises a shortcut to strong small language models. In this work, we examine this promise by pruning Llama-3.1-8B at pruning ratios of 0.5--0.8 with six methods spanning depth, width, and sparse granularities, under two controlled token-matched settings. (1) With the same training token budget, pruned initialization consistently outperforms random initialization. This shows that the parent model provides a strong starting point, although the advantage narrows as the training token budget grows and as the pruning ratio rises, nearly vanishing at the highest pruning ratio we study. (2) When training from scratch is instead given the full token budget consumed by the whole pipeline, pruning at finer granularities still retains an advantage, while coarser structured pruning can be matched or surpassed. This suggests that the parent model transfers knowledge that additional training tokens alone cannot fully recover, but only at fine granularity. Taken together, our results yield a clear recommendation: with a large pretrained model in hand and a limited training token budget, pruning is better than training from scratch; when the training budget is not limited, training from scratch can be competitive for coarser pruning, so a large pretrained parent is not always necessary.
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