I have dual vega 64s in Razer Core X's attached to my MBP 15 2017 (macos 10.13.6, blender 2.79b) One of the vegas drive a 4k display. When rendering regularly I get quite ok scaling and utilisation but in the viewport the egpus doesn't scale as expected. Let's say that a single attached egpu uses 80% of the gpu and when two are attached they both use less then 40% each as seen in the GPU history. I would have expected high utilsation of both and hence a smoother framerate in the viewport, now it feels almost slower.
Is there a known issue? Am I doing something wrong?
I think it might have to do with reading in the images from metal (for the rendering) to opengl (for the viewport) but we'll look into it.