GitLab

* have get_kth_microbatch deal with None batch

* broadcast based on tensor parallel rank

* dtype

* remove unnecessary .cuda()

Processes of tensor parallel rank != 0 doesn't need to prepare one or more `torch.utils.data.DataLoader` instances, which means the argument of `batch` of `get_kth_microbatch` function can be `None` but the current function implementation doesn't allow for it.