First of all determine, which device is our faster gpu. Then set the opencl_device_priority to prioritize the faster gpu e.g. opencl_device_priority=1,*/… and opencl_scheduling_profile=default.
I found (at least on my mac) the other options doesn’t respect the prioritizing
Btw: there’re plenty of opencl infos in the usermanual: “OpenCL scheduling profile” in the darktable usermanual