TernGrad: Ternary Gradients to Reduce Communication in Distributed Deep Learning

TL;DR

TernGrad introduces a ternary gradient approach using {-1, 0, 1} levels to significantly reduce communication overhead in distributed deep learning without sacrificing accuracy.

Contribution

The paper proposes TernGrad, a novel method that employs ternary gradients to accelerate distributed training while maintaining or improving accuracy.

Findings

TernGrad achieves no accuracy loss on AlexNet.

TernGrad causes less than 2% accuracy loss on GoogLeNet.

Significant speed gains are observed across various neural networks.

Abstract

High network communication cost for synchronizing gradients and parameters is the well-known bottleneck of distributed training. In this work, we propose TernGrad that uses ternary gradients to accelerate distributed deep learning in data parallelism. Our approach requires only three numerical levels {-1,0,1}, which can aggressively reduce the communication time. We mathematically prove the convergence of TernGrad under the assumption of a bound on gradients. Guided by the bound, we propose layer-wise ternarizing and gradient clipping to improve its convergence. Our experiments show that applying TernGrad on AlexNet does not incur any accuracy loss and can even improve accuracy. The accuracy loss of GoogLeNet induced by TernGrad is less than 2% on average. Finally, a performance model is proposed to study the scalability of TernGrad. Experiments show significant speed gains for various deep neural networks. Our source code is available.