Dear all:
I found I have a big problem in install cu90 version of pytorch:
/home/llq/conda/lib/python3.6/site-packages/torch/cuda/__init__.py:115: UserWarning: 
    Found GPU0 Tesla V100-SXM2-16GB which requires CUDA_VERSION >= 9000 for
     optimal performance and fast startup time, but your PyTorch was compiled
     with CUDA_VERSION 8000. Please install the correct PyTorch binary
     using instructions from https://pytorch.org
    
  warnings.warn(incorrect_binary_warn % (d, name, 9000, CUDA_VERSION))


I tried several ways to install such as:
conda install pytorch torchvision -c pytorch
conda install pytorch torchvision cuda90 -c pytorch
pip install torch....whl

No mater i try, the system will install cu80 for me.
I verified my pc installed cuda90 via nvcc -V.