AToM: Adaptive Token Merging for Efficient Acceleration of Vision Transformer

Recently, Vision Transformers (ViTs) have set a new standard in computer vision (CV), showing unparalleled image processing performance. However, their substantial computational requirements hinder practical deployment, especially on resource-limited devices common in CV applications. Token merging has emerged as a solution, condensing tokens with similar features to cut computational and memory demands. Yet, existing applications on ViTs often miss the mark in token compression, with rigid merging strategies and a lack of in-depth analysis of ViT merging characteristics. To overcome these issues, this paper introduces Adaptive Token Merging (AToM), a comprehensive algorithm-architecture co-design for accelerating ViTs. The AToM algorithm employs an image-adaptive, fine-grained merging strategy, significantly boosting computational efficiency. We also optimize the merging and unmerging processes to minimize overhead, employing techniques like First-Come-First-Merge mapping and Linear Distance Calculation. On the hardware side, the AToM architecture is tailor-made to exploit the AToM algorithm's benefits, with specialized engines for efficient merge and unmerge operations. Our pipeline architecture ensures end-to-end ViT processing, minimizing latency and memory overhead from the AToM algorithm. Across various hardware platforms including CPU, EdgeGPU, and GPU, AToM achieves average end-to-end speedups of 10.9$\boldsymbol{\times}$, 7.7$\boldsymbol{\times}$, and 5.4$\boldsymbol{\times}$, alongside energy savings of 24.9$\boldsymbol{\times}$, 1.8$\boldsymbol{\times}$, and 16.7$\boldsymbol{\times}$. Moreover, AToM offers 1.2$\boldsymbol{\times}$ 1.9$\boldsymbol{\times}$ higher effective throughput compared to existing transformer accelerators.