Diffy: a Déjà vu-Free Differential Deep Neural Network Accelerator

We show that Deep Convolutional Neural Network (CNN) implementations of computational imaging tasks exhibit spatially correlated values. We exploit this correlation to reduce the amount of computation, communication, and storage needed to execute such CNNs by introducing Diffy, a hardware accelerator that performs Differential Convolution. Diffy stores, communicates, and processes the bulk of the activation values as deltas. Experiments show that, over five state-of-the-art CNN models and for HD resolution inputs, Diffy boosts the average performance by 7.1× over a baseline value-agnostic accelerator [1] and by 1.41× over a state-of-the-art accelerator that processes only the effectual content of the raw activation values [2]. Further, Diffy is respectively 1.83× and 1.36× more energy efficient when considering only the on-chip energy. However, Diffy requires 55% less on-chip storage and 2.5× less off-chip bandwidth compared to storing the raw values using profiled per-layer precisions [3]. Compared to using dynamic per group precisions [4], Diffy requires 32% less storage and 1.43× less off-chip memory bandwidth. More importantly, Diffy provides the performance necessary to achieve real-time processing of HD resolution images with practical configurations. Finally, Diffy is robust and can serve as a general CNN accelerator as it improves performance even for image classification models.