TraNNsformer: Clustered Pruning on Crossbar-Based Architectures for Energy-Efficient Neural Networks

Abstract

Implementation of neuromorphic systems using memristive crossbar array (MCA) has emerged as a promising solution to enable low-power acceleration of neural networks. However, the recent trend to design deep neural networks (DNNs) for achieving human-like cognitive abilities poses significant challenges toward the scalable design of neuromorphic systems (due to the increase in computation/storage demands). Network pruning is a powerful technique to remove redundant connections for designing optimally connected (maximally sparse) DNNs. However, such pruning techniques induce irregular connections that are incoherent to the crossbar structure. Eventually, they produce DNNs with highly inefficient hardware realizations (in terms of area and energy). In this article, we propose TraNNsformer—an integrated training framework that transforms DNNs to enable their efficient realization on MCA-based systems. TraNNsformer first prunes the connectivity matrix while forming clusters with the remaining connections. Subsequently, it retrains the network to fine-tune the connections and reinforce the clusters. This is done iteratively to transform the original connectivity into an optimally pruned and maximally clustered mapping. We evaluated the proposed framework by transforming networks of different complexity based on multilayer perceptron (MLP) and convolutional neural network (CNN) topologies on a wide range of datasets (MNIST, SVHN, CIFAR10, and ImageNet) and executing them on MCA-based systems to analyze the area and energy benefits. Without accuracy loss, TraNNsformer reduces the area (energy) consumption by 28%–55% (49%–67%)of MLP networks and by 28%–48% (3%–39%) of CNN networks with respect to the original network implementations. Compared to network pruning, TraNNsformer achieves 28%–49% (15%–29%) area (energy) savings for MLP networks and 20%–44% (1%–11%) area (energy) saving for CNN networks. Furthermore, TraNNsformer is a technology-aware framework that allows mapping a given DNN to any MCA size permissible by the memristive technology for reliable operations.