MG-WFBP: Merging Gradients Wisely for Efficient Communication in Distributed Deep Learning

TL;DR

This paper introduces MG-WFBP, an optimized gradient merging method for distributed deep learning that reduces communication overhead and improves scalability, validated through extensive experiments on multiple GPU clusters.

Contribution

The paper proposes a novel gradient merging algorithm, MG-WFBP, that optimally combines short communication tasks to enhance distributed training efficiency.

Findings

MG-WFBP outperforms existing methods in scalability.

It effectively reduces communication time in distributed training.

Experimental results confirm improved training speed and scalability.

Abstract

Distributed synchronous stochastic gradient descent has been widely used to train deep neural networks (DNNs) on computer clusters. With the increase of computational power, network communications generally limit the system scalability. Wait-free backpropagation (WFBP) is a popular solution to overlap communications with computations during the training process. In this paper, we observe that many DNNs have a large number of layers with only a small amount of data to be communicated at each layer in distributed training, which could make WFBP inefficient. Based on the fact that merging some short communication tasks into a single one can reduce the overall communication time, we formulate an optimization problem to minimize the training time in pipelining communications and computations. We derive an optimal solution that can be solved efficiently without affecting the training performance. We then apply the solution to propose a distributed training algorithm named merged-gradient WFBP (MG-WFBP) and implement it in two platforms Caffe and PyTorch. Extensive experiments in three GPU clusters are conducted to verify the effectiveness of MG-WFBP. We further exploit trace-based simulations of 4 to 2048 GPUs to explore the potential scaling efficiency of MG-WFBP. Experimental results show that MG-WFBP achieves much better scaling performance than existing methods.