MaGe Linux Operations

Jun 20, 2026 · Artificial Intelligence

Custom PyTorch Dataset & DataLoader: Multiprocessing Optimization Guide

This article walks through diagnosing a severe GPU under‑utilization bug in an 8‑A100 training job, explains why the default Dataset/DataLoader setup stalls, and presents a step‑by‑step redesign using MapDataset or IterableDataset, WebDataset tar shards, tuned DataLoader parameters, worker‑level seeding, GPU‑side prefetching, and distributed sampling to boost GPU utilization from 5‑12% to over 85% while cutting epoch time from 40 h to 9 h.