Q1: If I have two models named A and B, both wrapped with DDP,  and loss = A(B(inputs)), will DDP work? It seems that gradients will be sync when loss.backward() is called.
Q2: If loss = A(B(inputs1), B(inputs2)), will DDP work ? The forward funciton of B is called twice . btw, I don’t know what does reducer.prepare_for_backward do…