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ScaleLong: Towards More Stable Training of Diffusion Model via Scaling Network Long Skip Connection
Zhongzhan Huang · Pan Zhou · Shuicheng Yan · Liang Lin

Tue Dec 12 03:15 PM -- 05:15 PM (PST) @ Great Hall & Hall B1+B2 #511
Event URL: https://github.com/sail-sg/ScaleLong »

In diffusion models, UNet is the most popular network backbone, since its long skip connects (LSCs) to connect distant network blocks can aggregate long-distant information and alleviate vanishing gradient. Unfortunately, UNet often suffers from unstable training in diffusion models which can be alleviated by scaling its LSC coefficients smaller. However, theoretical understandings of the instability of UNet in diffusion models and also the performance improvement of LSC scaling remain absent yet. To solve this issue, we theoretically show that the coefficients of LSCs in UNet have big effects on the stableness of the forward and backward propagation and robustness of UNet. Specifically, the hidden feature and gradient of UNet at any layer can oscillate and their oscillation ranges are actually large which explains the instability of UNet training. Moreover, UNet is also provably sensitive to perturbed input, and predicts an output distant from the desired output, yielding oscillatory loss and thus oscillatory gradient. Besides, we also observe the theoretical benefits of the LSC coefficient scaling of UNet in the stableness of hidden features and gradient and also robustness. Finally, inspired by our theory, we propose an effective coefficient scaling framework ScaleLong that scales the coefficients of LSC in UNet and better improve the training stability of UNet. Experimental results on CIFAR10, CelebA, ImageNet and COCO show that our methods are superior to stabilize training, and yield about 1.5x training acceleration on different diffusion models with UNet or UViT backbones.

Author Information

Zhongzhan Huang (Sun Yat-Sen University)
Pan Zhou (SEA AI Lab)

Currently, I am a senior Research Scientist in Sea AI Lab of Sea group. Before, I worked in Salesforce as a research scientist during 2019 to 2021. I completed my Ph.D. degree in 2019 at the National University of Singapore (NUS), fortunately advised by Prof. Jiashi Feng and Prof. Shuicheng Yan. Before studying in NUS, I graduated from Peking University (PKU) in 2016 and during this period, I was fortunately directed by Prof. Zhouchen Lin and Prof. Chao Zhang in ZERO Lab. During the research period, I also work closely with Prof. Xiaotong Yuan. I also spend several wonderful months in 2018 at Georgia Tech as visiting student hosted by Prof. Huan Xu.

Shuicheng Yan (National University of Singapore, Department of Electrical and Computer Engineering)
Liang Lin (Sun Yat-Sen University)

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