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Improving Post Training Neural Quantization:Layer-wise Calibration and Integer Programming

Most of the literature on neural network quantization requires some training of the quantized model (fine-tuning). However, this training is not always possible in real-world scenarios, as it requires the full dataset. Lately, post-training quantization methods have gained considerable attention, as they are simple to use and require only a small, unlabeled calibration set. Yet, they usually incur significant accuracy degradation when quantized below 8-bits. This paper seeks to address this problem by introducing two pipelines, advanced and light, where the former involves: (i) minimizing the quantization errors of each layer by optimizing its parameters over the calibration set; (ii) using integer programming to optimally allocate the desired bit-width for each layer while constraining accuracy degradation or model compression; and (iii) tuning the mixed-precision model statistics to correct biases introduced during quantization. While the light pipeline which invokes only (ii) and (iii) obtains surprisingly accurate results; the advanced pipeline yields state-of-the-art accuracy-compression ratios for both vision and text models. For instance, on ResNet50, we obtain less than 1% accuracy degradation while compressing the model to 13% of its original size. Our code is available in the supplementary material and would be open-sourced upon acceptance.

Reproducing the results

This repository is based on convNet.pytorch repo. please ensure that you are using pytorch 1.3+. To repreduce the results

sh scripts/advanced_pipeline.sh
sh scripts/light_pipeline.sh

To reproduce BERT-base results please follow the instruction in BERT-base folder