Attempting to run cuBLAS, but there was no current CUDA context!

UserWarning: Attempting to run cuBLAS, but there was no current CUDA context! Attempting to set the primary context... (Triggered internally at ../aten/src/ATen/cuda/CublasHandlePool.cpp:135.)
  return Variable._execution_engine.run_backward(  # Calls into the C++ engine to run the backward pass.

when I run nvidia-smi, I see that there is not gpu uses.

