GPU 0 is also used when running on other GPU

[MoeLau]

When running the test on 2nd GPU (with id 1) with caffe-RC3, the command nvidia-smi shows that both GPU 0 and 1 are being used. I think the thread for prefetching data (in InternalThread.cpp) uses GPU 0 in default. So how to set GPU ID of the prefetch thread ?
Processes: GPU Memory |
| GPU PID Type Process name Usage |
|=============================================================================|
| 0 28802 C /usr/bin/python 346MiB |
| 2 28802 C /usr/bin/python 7991MiB

Operating system:Ubuntu 14.04
Compiler: GCC
CUDA version (if applicable):8.0
CUDNN version (if applicable):8.0
BLAS:
Python or MATLAB version (for pycaffe and matcaffe respectively):Python