Liquid: Mix-and-Match Multiple Image Formats to Balance DNN Training Pipeline.

Today's deep neural network (DNN) training pipeline utilizes hardware resources holistically, including host CPUs and storage devices for preprocessing the input data and accelerators like GPUs for computing gradients. As the performance of the accelerator scales rapidly, the frontend data preparation stages are becoming a new performance bottleneck to yield suboptimal training throughput. Since the bottleneck in the pipeline may vary depending on hardware configurations, DNN models, and datasets, overprovisioning hardware resources for data preparation such as CPU cores and disk bandwidth is not a cost-effective solution. Instead, we make a case for leveraging multiple data formats, possibly with opposing characteristics in resource utilization, to balance the training pipeline. This idea is realized by Liquid, a new system for building an efficient training pipeline with multi-format datasets. Our evaluation on three distinct execution environments demonstrates that Liquid achieves up to 3.05x and 1.54x higher data preparation throughput on Cityscapes/CityPersons (PNG) and ImageNet (JPEG) datasets, respectively, over the baseline single-format pipeline. This leads up to 2.02x and 1.25x higher end-to-end geomean training throughput with no accuracy drop.