A High-Precision Flexible Symmetry-Aware Architecture for Element-Wise Activation Functions

Nonlinear activation functions (NAFs) play an essential role in deep neural networks (DNNs). Since versatile DNN accelerators need to support various DNNs which contain different NAFs, the flexible hardware design supporting those NAFs has become crucial. However, there are few high-precision flexible hardware architectures, and the symmetries of different NAFs have not been fully studied. This paper proposes a high-precision symmetry-aware architecture based on piecewise linear approximation. Through the reconfigurable data path, the architecture can support various typical NAFs. The efficient non-uniform segmentation scheme is proposed to achieve high precision for each NAF. Besides, the utilization of unified symmetry for NAFs can save half the memory. To reduce the computational cost, a 25×18 DSP is shared by two INT 7×9 multipliers with two independent inputs. The architecture is implemented on Xilinx ZC706 at a frequency of 410MHz. Compared with the state-of-the-art flexible nonlinear core, our flexible architecture costs fewer hardware resources with higher precision. Applying the design to BERT-BASE, MobileNetV3, and EfficientNet-B3 on the PyTorch platform, experimental results show that the accuracy loss is either 0 for BERT-BASE, or 0.002% for EfficientNet-B3. For MobileNetV3, the accuracy is even improved by 0.01%.