that is a cuda enviroment variable.
It’s not pytorch.
What it means is that you can call any bash command preceded by that. It basically manages which devices the called process can see.
So in your case it means that your python kernel can only see one of the gpus. Both if you set 0,1. But it doesn’t mean that pytorch is gonna train on both automatically.
To train on several gpus you should use modules like https://pytorch.org/docs/stable/generated/torch.nn.DataParallel.html 6