用小模型引导大模型,高效剪枝视觉令牌,兼顾速度与精度。
A Stitch in Time Saves Nine: Small VLM is a Precise Guidance for Accelerating Large VLMs

- 用小模型的全局注意力图指导大模型的视觉令牌剪枝。
- 在保留91%视觉令牌精度的前提下,实现高达91%的剪枝率。
- 无需训练,支持动态调用大模型,适合资源受限场景。
视觉语言模型(VLM)在多模态任务中表现优异,但大型VLM因处理大量视觉令牌而面临显著效率挑战。现有加速方法依赖特定层的注意力图评估令牌重要性并剪枝,但研究发现:(i) 局部注意力信息不足以准确识别关键视觉令牌,尤其在低保留率时性能下降;(ii) 全局注意力图(跨所有层聚合)更有效保留关键令牌,但需完整推理,计算开销大;(iii) 小型VLM的全局注意力图与大型VLM高度相似。基于此,提出无需训练的SGL方法:利用小型VLM的聚合注意力图指导大型VLM剪枝,并引入早停机制,仅在必要时调用大模型,实现精度与计算量的更好平衡。在11个基准上验证,最高可实现91%视觉令牌剪枝率,同时保持竞争力性能。
原文摘要 · Abstract (English)
Vision-language models (VLMs) have shown remarkable success across various multi-modal tasks, yet large VLMs encounter significant efficiency challenges due to processing numerous visual tokens. A promising approach to accelerating large VLM inference is using partial information, such as attention maps from specific layers, to assess token importance and prune less essential tokens. However, our study reveals three key insights: (i) Partial attention information is insufficient for accurately identifying critical visual tokens, resulting in suboptimal performance, especially at low token retention ratios; (ii) Global attention information, such as the attention map aggregated across all layers, more effectively preserves essential tokens and maintains comparable performance under aggressive pruning. However, the attention maps from all layers requires a full inference pass, which increases computational load and is therefore impractical in existing methods; and (iii) The global attention map aggregated from a small VLM closely resembles that of a large VLM, suggesting an efficient alternative. Based on these findings, we introduce a \textbf{training-free} method, \underline{\textbf{S}}mall VLM \underline{\textbf{G}}uidance for accelerating \underline{\textbf{L}}arge VLMs (\textbf{SGL}). Specifically, we employ the attention map aggregated from a small VLM to guide visual token pruning in a large VLM. Additionally, an early exiting mechanism is developed to fully use the small VLM's predictions, dynamically invoking the larger VLM only when necessary, yielding a superior trade-off between accuracy and computation. Extensive evaluations across 11 benchmarks demonstrate the effectiveness and generalizability of SGL, achieving up to 91\% pruning ratio for visual tokens while retaining competitive performance.
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