Some computers choose not to use the GPU when running a UDK game

I have a fair amount of players that report low fps, then it turns out that their GPU is not being used and they need to tell the drivers to use it for the game in their nvidia control panel (which then fixes the low fps). Seems to only be an issue for nvidia systems.

Does anyone know how to get around this problem?

Well you can’t run it without a GPU, so most likely what you mean is that they have a system that has both an integrated Intel GPU and a dedicated Nvidia GPU and it’s not using the right GPU. You can’t control that in the software, it’s controlled by drivers and that’s pretty typical. It’s supposed to use the right GPU for whatever you’re doing but I haven’t known it to work that well. If users have that issue, you can just recommend that they adjust the settings in the Nvidia Control Panel to assign the Nvidia GPU to be used instead of the Intel GPU. Again, you can’t change it in your game, it’s a system configuration thing.

So if you have disabled the onboard GPU and tell it to use the slot card GPU, it till finds the main board GPU? and can not find slot card GPU that was enabled?

From my tests you get the best performance by going into the Nvidia Control Panel and setting it to use the Nvidia GPU as the global default.
There’s a setting there where you can assign a GPU to a specific program, but in my tests it didn’t perform as well that way as it does if you just don’t use the Intel GPU at all and have it use the Nvidia GPU for everything. This will impact battery life if it’s a laptop though.
If they’re still having issues with it not using the right GPU then something else is going on.

allowing the game to select which GPU to use is something we (others in my team) implemented in a previous project but it was UE4 and I don’t think the solution came out of the box with the engine.
In UE3? might be doable with source access. UDK? for sure not

I believe you’re stuck having to communicate it to your players via a FAQ or similar, and do it via the nvidia control panel