At least you get F12 render ustilizing all GPU’s at max. For my Setup I get what you get for Progressive. The GPU’s are simply not used to the max.
For all
For windows 10, note that you have to click the “3D” text in the task manager and select Compute3 (in my case) to see actual GPU usage. Though it’s acurate as Compute isn’t 3D usage, but usage is usage so it causes confusion, and the feature is somehwat hidden.
And as some use GPU-Z that will show actual usage all the time.
I know this is an old thread, but I’ve made an add-on which somewhat adresses this issue. With multiple gpus of different performance, the viewport rendering performance is actually worse than straight up just using only the fastest gpu for cycles viewport rendering, but final render greatly benefits from as many gpus as it can get. My add-on lets you indepently choose devices for viewport and final rendering. It’s also free.
Check it out here:
