So I have a laptop with 2 GPUs: an Intel HD 520 and a Geforce 940MX.
In the case of 2.79, if I had set Blender to run on the nVidia GPU in the NV control panel, there was a horrible GUI lag when there was rendering in progress using Cycles. All GUI elements took 2-3 seconds to react to mouse hover and mouse clicks. This is completely normal, of course, because the GPU that is used to render the GUI is also being used to render the image in Cycles. And of course with CPU rendering, this GUI lag didn't happen.
If I had set 2.79 to use the Integrated Intel HD GPU, there was no GUI lag because only Cycles render engine used the nVidia GPU and the rest of Blender used the Intel HD GPU.
Now, in 2.80 I am having the same issue, but this time, configuring in the NV control panel to run Blender on the Intel GPU doesn't help. The GUI still lags like hell, and it's almost unusable because I can't make fast changes, tinker with materials etc. while it's rendering. (In 2.80 CPU rendering still works fine as expected.)
Same thing with GPU and CPU+GPU rendering (GPU Compute).
I have Geforce 436.30 drivers (most recent).
940MX is set to 'Maximum Performance' in NV Control Panel, other settings are default.
Windows 10 v1903.
Blender 2.80 most recent stable version.
Was there a change in how the GUI gets rendered in 2.8 or something? If anyone can help, I would really appreciate.