How to train the convnet on multiGPUs?

Execuse me, I have some question about convnet.
I have train the convnet on multiGPUs by using "boards=01", however, the result is the train only on one board rather than two boards. I get the result by using "nvidia-smi" and find that there two processes but only one of the boards is used.
So I want to know how to train the model by data parallel and model parallel using multiGPUs, do I have to modify something?
My mailbox is 854659608@qq.com and look forward to your response.
Thank you very much.