How to use two GPUs on a single node?

I need to render a large scale data, so I need to use two GPUs, but I found that one of the GPUs is not used, and the frame rate is very low when only using one GPU. Is there a way to use two GPUs together?

When I was reading the 9.0 release-note, I found that the Nvidia Index plugin might be effective. I haven’t found a way to use it in Paraview, so I’m here to ask for help. Hope someone can help me!