Update for selecting a specific GPU

README.md

@@ -35,14 +35,18 @@ responsibly. If your computations do not require all the available GPUs consider
 specifying $CUDA_VISIBLE_DEVICES variable in your environment, e.g., to set only
 GPU with index 1 visible:
 ```
+export CUDA_DEVICE_ORDER=PCI_BUS_ID
 export CUDA_VISIBLE_DEVICES=1
 ```
 or in python
 ```python
 import os
+os.environ["CUDA_DEVICE_ORDER"]="PCI_BUS_ID"
 os.environ["CUDA_VISIBLE_DEVICES"]="1"
 ```
 
+(The environment variable $CUDA_DEVICE_ORDER makes the GPU IDs to be identical
+with the command nvidia-smi.)
 Some frameworks (e.g. TensorFlow) are greedy and they allocate resources on all
 the available devices while utilizing only one of them effectively. By
 explicitly specifying which GPU device you need you do not block other users