Slow Viewport when Arnold Render View Window is open (not rendering)

[bhoyle]

Maya 2020.4
MtoA 5.0.0.2
RTX3080
AMD Ryzen 9 5900X 12-Core

I recently ran into the problem that GPU batch render starts to clogg the GPU memory with every new rendered frame. I updatet MtoA to 5.0.0.2 which allowed me to render more frames but still fills up GPU memory with every frame until the render aborts.

Not sure if this happened with the update to 5.0.0.2 but I´ve now witnessed a seperate issue regarding the Viewport:
As soon as you hit render once (GPU or CPU does not matter) the Viewport becomes very slow / sluggish. This behaviour persists even while IPR is stopped.
Viewport only becomes responsive again after closing the Arnold Viewport Window.

The sluggishness of the viewport is even more apparent when scrubbing the timeline. (only a simple object translation and rotation in my case). Moving the camera is also affected but not as much as scrubbing the timeline.

I´ve read similar threads here where this was allegedly fixed many versions of MtoA earlier.
https://answers.arnoldrenderer.com/questions/23364/arnold-6-gpu-feedback-to-viewport-so-slow.html
Has this problem now been re-introduced?

[thiago.ize]

If you lower the number of render threads by 2 or 4 does it fix this sluggishness? In ARV you can also use "Render/Save UI Threads" to do this.

[bhoyle]

@Thiago Ize Thanks and I might be mistaken, but since I use GPU most of the time and render threads refers to CPU this will not help(?). More importantly the viewport is sluggish even when rendering is stopped/paused, so there should not be any real performance problem when the system is not rendering anything.

[Stephen.Blair]

CPU is still used for some things, even when you use Arnold GPU.

And if Maya is sluggish because Arnold is using all the cores, then it must be CPU stuff using the cores, so reducing the number of threads is worth a try...