Consider increasing the value of the `num_workers` argument` in the `DataLoader` init to improve performance.

PyTorch Lightning を使っていてよく分からない warning が出る。
https://github.com/PyTorchLightning/pytorch-lightning/blob/0.7.6/pytorch_lightning/trainer/data_loading.py#L96-L99

if isinstance(dataloader, DataLoader) and dataloader.num_workers <= 2 and not on_windows:
    rank_zero_warn(f'The dataloader, {name}, does not have many workers which may be a bottleneck.'
                   ' Consider increasing the value of the `num_workers` argument`'
                   ' in the `DataLoader` init to improve performance.')

の部分だけど、3 以上にする必要があるのだろうか・・・？