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keywords:
cv
language and vision
Multimodal large language models (MLLMs) enhance their perceptual capabilities by integrating visual and textual information. However, the massive number of visual tokens incurs a significant computational cost. Existing analysis of the MLLM attention mechanisms is unfortunately shallow, leading to coarsely specified token pruning strategies that are unable to strike a balance between speed and accuracy. In this paper, we conduct a comprehensive investigation of MLLM attention mechanisms with LLaVA as the case study subject. We find that numerous visual tokens and partial attention computations are ineffective during the decoding process. Based on empirical insights, we propose Spatial-Temporal Visual Token Trimming ($\textbf{ST}^{3}$) with two primary components: 1) $\textit{Spatial}$: Progressive Visual Token Pruning ($\textbf{PVTP}$) and 2) $\textit{Temporal}$: Visual Token Annealing ($\textbf{VTA}$). ${\bf PVTP}$ eliminates inattentive visual tokens as layers deepen, while ${\bf VTA}$ dynamically reduces the number of visual tokens in each layer as the generated tokens grow. Together, these techniques achieve around $\mathbf{2\times}$ faster inference with only about $\mathbf{30}$% KV cache memory compared to the original LLaVA, while maintaining consistent performance across various datasets. Crucially, our proposed mechanisms are designed to be plug-and-play, allowing seamless integration with existing pre-trained MLLMs without incurring any additional training costs.