USD: Very poor USD point instancing performance

[stehrani3d]

Hi, I am doing some testing of potential instancing workflows in Maya and I am running into performance issues with point instanced USD geometry. The workflow is basically this:

• Models are exported out of Maya with V-Ray materials as "intermediate" USD files
• Models are then re-exported as "final" USDs from Houdini using its Component Builder workflow (for creating the proxy purpose, setting up variants, etc)
• These models are then scattered/instanced in Houdini and the scatter is then exported as a USD file to be rendered in Maya

USD_Instancing.zip (400MB)

I like this approach since I can take advantage of the scatter capabilities of Houdini, and V-Ray's material schema allows for round-tripping of materials back into Maya. Great!
The issue is that I am seeing very long geometry compilation times in Maya. In other words, the time-to-first-pixel is awful. On top of that, once the render has finished, the Maya session just sits there locked up, with two CPU cores doing who-knows-what.
Below are some statistics:

Number of instances:
Sink - 90K
Jackhammer - 330K
Grass - 4.5M

Time to First Pixel:
Maya - 12:21
Houdini - 0:45

"Unloading" Time:
Maya - 8:48
Houdini - NA

Maya 2023.2
Maya USD 0.19
V-Ray 6 (v6.00.02)

Houdini 19.5
V-Ray 5 (v5.20.24)

This machine:
Windows 10 Pro
3960X Threadripper (I'm rendering strictly in CPU mode)
256GB RAM

Where does this difference in performance come from? If I remember correctly V-Ray for Maya uses a USD Procedural whereas USD goes through Hydra in V-Ray for Houdini. Is this even a V-Ray issue or is it related to Maya USD itself?
Thank you.

[stehrani3d]

I have tried bumping the version number for everything:

Maya 2023.3
Maya USD 0.20
V-Ray 6, hotfix 1 (v6.00.03)

Unfortunately no change in performance. And I've noticed a strange behavior that I missed last time: The "Compiling geometry" step gets longer with subsequent renders. The first time geometry compilation might take 7 minutes, the next time 12 minutes, and then 16 minutes after that. No change to the scene or camera, just hitting render again. Very odd...
I have also tried loading the USD stage through Bifrost. Same slow performance.

Any ideas?

[afitch]

Hi!

Is it possible to try Vray 5 for Maya? Haven't used USD in vray5 so I'm unsure if it's properly supported.
But have a lot of performance issues in vray6 in general, that I didn't have in Vray5, so it could be interesting to see if there is a difference...

//Troels

[SGesheva]

Thanks for the report and provided scene stehrani3d.
We were able to reproduce the slow Compiling geometry part and are looking into the increasing times with subsequent renders. I've logged it for developer investigation (internal bug-tracker id: VMAYA-11792).

[stehrani3d]

Excellent, thank you for taking a look and passing it on Svetlana!
Afitch, thank you as well. I tried V-Ray 5 but I don't believe it supports the newest versions of Maya USD because it ignored all the USD geo.

[stehrani3d]

Hello team, have there been any updates regarding this issue? We are once again dealing with some USD instances and running into the same performance bottleneck. We did some testing with Arnold using this same test scene, and it has no issues with instance translation, starting the render in less than half a minute. That leads us to think the issue is the V-Ray USD procedural rather than anything inherent to the Maya USD plugin. This latest round of testing was performed with Maya 2024 and V-Ray 6 update 1, FYI.

[SGesheva]

No updates yet, I'm afraid, but it's on the To Do list. I'll increase its priority and let you know when there's any progress.

[SonyBoy]

Is this a still from The Matrix: Regardened?