Filter Pre-Pruning for Improved Fine-tuning of Quantized Deep Neural Networks

TL;DR

This paper introduces a pruning method called PfQ to improve the fine-tuning of quantized deep neural networks by removing filters that hinder accuracy recovery, leading to better performance without extra parameters.

Contribution

The paper proposes a novel pruning technique, PfQ, that enhances quantized DNN fine-tuning by addressing batch normalization issues without additional hyper-parameters.

Findings

Achieves higher accuracy with similar model size compared to conventional methods

Effectively mitigates batch normalization effects during quantization

Improves fine-tuning performance of low-bit quantized DNNs

Abstract

Deep Neural Networks(DNNs) have many parameters and activation data, and these both are expensive to implement. One method to reduce the size of the DNN is to quantize the pre-trained model by using a low-bit expression for weights and activations, using fine-tuning to recover the drop in accuracy. However, it is generally difficult to train neural networks which use low-bit expressions. One reason is that the weights in the middle layer of the DNN have a wide dynamic range and so when quantizing the wide dynamic range into a few bits, the step size becomes large, which leads to a large quantization error and finally a large degradation in accuracy. To solve this problem, this paper makes the following three contributions without using any additional learning parameters and hyper-parameters. First, we analyze how batch normalization, which causes the aforementioned problem, disturbs the fine-tuning of the quantized DNN. Second, based on these results, we propose a new pruning method called Pruning for Quantization (PfQ) which removes the filters that disturb the fine-tuning of the DNN while not affecting the inferred result as far as possible. Third, we propose a workflow of fine-tuning for quantized DNNs using the proposed pruning method(PfQ). Experiments using well-known models and datasets confirmed that the proposed method achieves higher performance with a similar model size than conventional quantization methods including fine-tuning.