Optimizing Multi-GPU Parallelization Strategies for Deep Learning Training

Deploying deep learning (DL) models across multiple compute devices to train large and complex models continues to grow in importance because of the demand for faster and more frequent training. Data parallelism (DP) is the most widely used parallelization strategy, but as the number of devices in data parallel training grows, so does the communication overhead between devices. Additionally, a larger aggregate batch size per step leads to statistical efficiency loss, i.e., a larger number of epochs are required to converge to a desired accuracy. These factors affect overall training time and beyond a certain number of devices, the speedup from DP scales poorly. This work explores hybrid parallelization, where each data parallel worker comprises more than one device to accelerate each training step by exploiting model parallelism. We show that at scale, hybrid training will be more effective at minimizing end-to-end training time than exploiting DP alone. We project that, for Inception-V8, GNMT, and BigLSTM, the hybrid strategy provides an end-to-end training speedup of at least 26.5%, 8%, and 22%, respectively, compared to what DP alone can achieve at scale.