Arnold 7.2.1.0 laggy on Threadripper 3990x

[jdm_007]

Arnold 7.2.1.0 is laggy on AMD 3990x CPU with 64-cores in Maya 2024 (Windows 11).

i have to reduce the number of threads manually to 64 to keep interactivity. 
am I the only one with this issue? I saw an old thread in the 3ds max forum where someone from Autodesk mentioned it was fixed in Arnold 6.0.4 so I wonder if it is a regression?

thank you

[thiago.ize]

For me 128 threads performs better than 64 (actually 125 because I told ARV to reserve 3 threads for UI). I have the exact same setup as what you listed except that I'm still on Windows 10.

If you go from 64 to 65 threads does it get noticeably worse? Do you have other applications consuming CPU resources? Is this all scenes or does it require something in particular to trigger it?

If you disable in ARV the "Render/progressive Refinement" and instead set the Camera AA to some small value (maybe 1, -1, or -3, for instance.) so that it feels interactive, does that fix the lag with extra threads? If it does, then I suspect this is because with 128 threads Arnold is trying to render at higher AA and this takes longer so the FPS goes down, with the flipside being that it looks nicer.

[jdm_007]

Going to 65 is still ok and does not slow down the computer, and also going to 125 is a bit better than 128, but even at 125, it looks like the threads priority are too high and bring the whole computer to its knees, Windows 11 gets slow overall so it’s not just the IPR getting laggy, it’s everything, with frequent lock ups of the Maya UI, even on very simple scenes.

The interesting bit is that it does get slower and less interactive in the first 10 seconds of the render, then it gets a bit better.

 I don’t have anything else running in the background. Now, to your point I don’t recall having these slow downs on Windows 10, so I wonder if it is a specific issue with 11.

[thiago.ize · Accepted solution]

Windows 11 has a different way of scheduling threads and handling priorities, so it could be OS dependent. That it's making the rest of the computer feel laggy, makes it still more likely that it could be OS thread scheduler related. Until we can reproduce/fix this on our end, hopefully there's some number of threads between 64 and 125 that gives you better results and you can take advantage of in the meantime?

[jdm_007]

Thanks Thiago. I can definitely find a middle ground between lag and performance. Glad that you are looking into it, so long as it can be evaluated and addressed at some point, I am good.