USRP underrun, overrun

Now I have problems with uU and uO

Are they related with a computational power? (CPU clock, RAM, running on
VM?)

Now I’m using GRC on Ubuntu on VMWare on MacBook Pro

Everytime I run a flow graph, I get tons of uUuUuUuUuUuUuOuOuOuOuOuOuOuO

Are they related with a computational power? (CPU clock, RAM, running on
VM?)

Yes.
What are you doing?
It means a) the USRP wants samples and the PC is to slow in providing
them
or b) the USRP is sending samples and the PC is too slow in receiving
them.