how to test in multiple GPU

[GraceZhuuu]

I wrote a multi-GPUs test script with reference to basic SR. Although it can run, only one GPU is used.

PYTHONPATH="./:${PYTHONPATH}" \
CUDA_VISIBLE_DEVICES=0,1,2,3 \
python -m torch.distributed.launch --nproc_per_node=4 --master_port=4321 DiffIR/test.py -opt options/test_DiffIRS2.yml --launcher pytorch