multi-gpu support

[GritLs]

Thank you for your outstanding work on this project and for making it open source!

I would like to inquire if multi-GPU training is supported. I noticed a switch on line 78 of run.py that controls whether to use multi-GPU. However, when I set this option to true and rerun the script, the process seems to get stuck, and the terminal outputs the following message:

Could you please assist me with this issue? Thank you!