Arnold not using all cpu-threads consistently during rendering (3ds Max)

[DavidMarchal8279]

Hi all,
I'm currently evaluating 3ds Max 2019 for purchase (well, subscription). I've been out of 3ds max for a couple of years and I'm getting back into 3D rendering. Currently I'm testing toon (NPR) rendering in Arnold. With my system (AMD 2990WX-128GB-Windows 10), I have 32 cores and 64 threads to use. By rendering the same file (a high res car model), I see the usage of threads vary between 100% and 10% and this of the same scene! So by rendering the scene (thread usage for example 95%), closing 3DS max and reopening the scene and render (thread usage only 30%), the thread usage varies greatly. This shouldn't be the case imo.
So I'm taking about the thread usage when starting the actual render (not the preparing of the model/scene). I've noticed this with a couple of scenes so this problem isn't limited to one specific scene.
So the problem is with Arnold or 3DS Max I assume?
Has somebody seen this before? Is this a known issue?

I'm running 3ds Max 2019 trial with Arnold 2.3.37
I've also varied the bucket sizes between 32 and 512, but no change in behaviour (except impact on render times ;-).
I've varied the resolution size (up to 11.000x7400 pixels), but no change in behaviour.

I've attached a log file when I got 67% usage of the threads. And also a screenshot of the Taskmanager to indicate the load on the threads/cores. This particular scene has 5 lights, but I've got the same problem with 1 light-scenes.

Any help would be greatly appreciated and many thanks in advance!

Best regards,

David

arnold-cputhread.txt

arnold-65percent-graph.jpg

[cmpxchg8b]

Try increasing the texture cache size. I think the default is 2GB, but I've seen very similar behavior when the scene textures exceed the cache size by some large amount (CPU usage will drop down to 5-10% while Arnold loads in textures, then jump up to 100%, then back down while it loads in more textures, etc, etc).

-CMPX

[DavidMarchal8279]

Thank you I'll try that. Although I only have 1 small texture in this scene, I hope this works. Thanks again!

[DavidMarchal8279]

Unfortunately it didn’t help. Also playing with the other texture settings didn’t solve the problem...

[maxtarpini]

as a testing scenario here you need to have a consistent scene where all the buckets take generally the same 'long enough' time to process the pixels, have the same geometry and textures load, and also a resolution that is a multiple of your bucket size in both x/y and perhaps is also a multiple of your threads count.

in the while however I can't resist to say that if you're getting back to 3D with that kind of machine and you deliberately choose 3dsmax and windows .. that's what your deserve 🙂

[DavidMarchal8279]

The problem has been solved.

By reducing the Filter width of the Contour-filter (which is required for Edges to render for Toon) all threads are used to their fullest extent.

@Max Tarpini I've been using 3ds Max from when it was still called 3D Studio in the early days, so I'm used to some strange behaviour 😉

[Stephen.Blair]

We were just going to suggest it might be toon or contour, and to test with different shaders...

[gimble]

Hi, I'm having the same problem in Arnold 4.1.0 for Maya. It only happens in the Arnold render view. When batch rendering all threads are used. I think it's a bug. A way to fix it is to refresh the renderer by unchecking and re-checking the Autodetect Threads tab in the System panel of the render settings. Go to task manager in windows to check all threads are working during render. I'm guessing in Max there's a similar checkbox. Annoying but works for me. Also I find deleting my Maya prefs helps.