SimulationApp class physics_gpu and multi_gpu


I’m little confuse with the SimulationApp usage.

According to the doc:

There are two params: physics_gpu, multi_gpu.

I would like to ask whether these two parameters are for physical simulation and rendering respectively?
Otherwise, in the case of multiple GPU, if multi_gpu is set to true, what should physics_gpu be set to?

Another question is that:
Isaacsim will automatically call multiple GPUs.
Does the call here refer to using multiple GPUs for rendering?
Will multiple GPUs be used for physics engine calculations at the same time, or will only the first GPU be used for physics engine calculations?

Can I get some help?
Thanks in advance.