If you are using the iter/next approach, the DataLoader iterator might already start preloading the data once you call the next op on it, so you could potentially overlap the loading of the first batches with other operations in your main script.
Thanks @ptrblck, I can confirm that in the iter/next approach, the dataloader behaves as expect and preloads future batches when number of workers > 0. My observation is based on a vanilla dataloader from torch.