改进神经网络权值初始化,显著提升量化模型精度。
Starting Positions Matter: A Study on Better Weight Initialization for Neural Network Quantization
- 用图超网络预测量化模型参数,实现更鲁棒的初始化。
- 4比特量化下准确率明显提升,2比特也能保持优于随机的性能。
- 首次系统研究量化初始化问题,适合做模型压缩的工程师。
深度神经网络(DNN)量化是实现快速高效推理的关键技术,常通过正则化、量化感知训练等方法提升精度与鲁棒性。然而,对训练初始条件的优化研究极少。我们系统研究了不同权重初始化对常见高效CNN结构的影响,发现初始方法显著影响量化后的性能。提出基于图超网络(GHN)的新初始化方法:先在浮点预训练中生成量化鲁棒参数,再通过微调GHN以预测量化图参数(GHN-QAT),进一步提升精度。实验显示,该方法在4比特量化下有显著增益,2比特时仍优于随机初始化。这是首个关于量化感知权值初始化的深入研究,为量化模型设计提供了新思路。
原文摘要 · Abstract (English)
Deep neural network (DNN) quantization for fast, efficient inference has been an important tool in limiting the cost of machine learning (ML) model inference. Quantization-specific model development techniques such as regularization, quantization-aware training, and quantization-robustness penalties have served to greatly boost the accuracy and robustness of modern DNNs. However, very little exploration has been done on improving the initial conditions of DNN training for quantization. Just as random weight initialization has been shown to significantly impact test accuracy of floating point models, it would make sense that different weight initialization methods impact quantization robustness of trained models. We present an extensive study examining the effects of different weight initializations on a variety of CNN building blocks commonly used in efficient CNNs. This analysis reveals that even with varying CNN architectures, the choice of random weight initializer can significantly affect final quantization robustness. Next, we explore a new method for quantization-robust CNN initialization -- using Graph Hypernetworks (GHN) to predict parameters of quantized DNNs. Besides showing that GHN-predicted parameters are quantization-robust after regular float32 pretraining (of the GHN), we find that finetuning GHNs to predict parameters for quantized graphs (which we call GHN-QAT) can further improve quantized accuracy of CNNs. Notably, GHN-QAT shows significant accuracy improvements for even 4-bit quantization and better-than-random accuracy for 2-bits. To the best of our knowledge, this is the first in-depth study on quantization-aware DNN weight initialization. GHN-QAT offers a novel approach to quantized DNN model design. Future investigations, such as using GHN-QAT-initialized parameters for quantization-aware training, can further streamline the DNN quantization process.
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