reduce_scatter raises a RuntimeError

[garrett361]

Hello, cross posting from ipex #647: torch-ccl does not support torch.distributed.reduce_scatter, despite the claims in the docs.

For instance, in 2.1.300+xpu we have:

torch-ccl/src/ProcessGroupCCL.cpp

Lines 871 to 877 in b9ce713

	c10::intrusive_ptr<C10D_Work> ProcessGroupCCL::reduce_scatter(
	std::vector<at::Tensor>& /* unused */,
	std::vector<std::vector<at::Tensor>>& /* unused */,
	const ReduceScatterOptions& /* unused */)
	{
	TORCH_CHECK(false, "ProcessGroupCCL does not support reduce_scatter");
	}

where the TORCH_CHECK line raises a RuntimeError.

See the ipex ticket for more details and code to reproduce the error.