I made a GUI library for games. My test demo runs at 60 fps. When I run this demo with the static version of my library it takes 2-3% cpu in taskmanager. When I use the DLL vers
If you call DLL-functions they cannot be inlined for a caller. You should think a little about your DLL-boundaries.
May be it is better for your application to have a small bootstrap exe which just executes a main loop in your DLL. This way you can avoid much overhead for function calls.