Super slow when running demos


I am using a 1080Ti graphic card. The demos are running super super slow.
It even took a long time to show the GUI visualization window.
I followed the installazation guide from github using : python3 -m pip install taichi

Here is of configuration of my PC :
Ubuntu 18.04
CUDA 10.1
demos running : python3
the other demos are almost the same.

I am not sure what happened. Could you help me on this?
Thank you very much.