指定GPU 一开始：
CUDA_VISIBLE_DEVICES=1 python test.py
安装指南：
https://blog.ailemon.me/2017/06/06/install-tensorflow-gpu-on-ubuntu-linux/
~/.bashrc 里面的东西
#cuda settings
export PATH=$HOME/cuda-8.0/bin:$PATH
export CPATH=$HOME/cuda-8.0/include:$CPATH
export LIBRARY_PATH=$HOME/cuda-8.0/lib64:$LIBRARY_PATH
export LD_LIBRARY_PATH=/$HOME/cuda-8.0/lib64:$LD_LIBRARY_PATH
