Toward Efficient Retraining: A Large-Scale Approximate Neural Network Framework With Cross-Layer Optimization

Leveraging approximate multipliers in approximate neural networks (ApproxNNs) can effectively reduce hardware area and power consumption, making them suitable for edge-side applications. However, the propagation of layer-by-layer errors limits the application of approximate multipliers to large-scale ApproxNNs and complex tasks. Currently, retraining techniques that consider approximate multiplication errors are commonly used to compensate for the accuracy loss. However, due to the irregularity of the errors introduced by approximate multiplier, it is difficult for the existing generic acceleration hardware (e.g., GPU) to efficiently simulate its function and accelerate retraining, which thereby leads to a huge retraining overhead in ApproxNNs’ application. In this article, we propose an ApproxNN framework that introduces errors with regular and controlled positions for high-efficiency retraining of large-scale ApproxNNs. An approximate multiplier design that matches this framework is also presented to verify the effectiveness of the proposed ApproxNN framework. Experiment results demonstrate that the proposed ApproxNN framework is able to achieve up to $46\times $ speedup in retraining, and the proposed approximate multiplier reduces area/power-delay product (PDP) by 31%/63% compared to the exact multiplier. Compared with the floating-point neural network (NN) model, an accuracy decrease of only 1.13% is achieved when applied to ResNet50 on ImageNet dataset with only 15-epochs retraining, which surpasses other state-of-the-art designs.