Chaos Corona for 3ds Max > [Max] I need help!

CPU usage drops to ~10%

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Mirage Studio:
Hi,

I searched around and found a few old posts/articles (over 2 years old) about people experiencing CPU drops and it was related mostly to software updates and Windows 11 support. I would think that this is now up to date so I'm curious now if any light can be shed on my issue.

Quick look:
Ryzen threadripper 3970x
128gb 3600mhz ddr4 ram
Windows 11 (up to date)
Corona Renderer 11 hotfix 2
3dsmax 2024
Water cooled (max temp about 75C under full load)

As the title says, I'm getting CPU drops from 100% down to around 10% and then it stays at 10%. Usually if i reopen a file it will give me a couple tries at 100% but then seemingly at random the next one will drop to 10% usage. It seems to spread across cores so it's not just dropping to a single thread or something as far as I can tell. I've tried with different versions of 3dsmax and Corona and it seems to be system wide which leads me to believe it's a hardware issue.

I've been using this machine for about 5 years with no issues and only recently have had this come up. Even small scenes that utilize only 30% ram it happens so it's not me maxing ram out, I'm very familiar with that but this isn't it. I've considered picking up another 128gb just to be sure though.

I thought I figured it out when I disabled the caustics solver which seemed to resolve the issue at first but then it returned even with it turned off. It sometimes helps but inevitably the problem persists.

Any ideas?

Avi:
Hi,

Can you let me know if you see the same CPU usage drop behavior with a simple max file with few boxes and geometric shapes?

At what stage of rendering does CPU usage drop? Such as during UHD cache calculation?

By any chance you are using CoronaAO and CoronaRoundEdges in your scene?

Can you try using Corona benchmark to see if you can still see CPU usage drop with it? https://corona-renderer.com/benchmark

I understand that you have already tried turning off caustics but can you double check it again that turning it off does not fix the problem for you?

Can you make sure that your windows is uptodate? Settings > Update & Security > Windows Update

Can you also check if your power settings are set to high performance? Control Panel > Hardware and Sound > Power Options>High performance.

Mirage Studio:
Hi Avi,

Thank you for the response.

It seems to happen with more complex scenes only that I've noticed. It also happens different between 3dsmax instances. For example, if one scene drops down to 10% CPU I can run another scene at 100% after. I'll maybe get 1 or 2 interactive render tests before that scene then drops too.

I've noticed it starting at parsing mostly. A scene that should take 10 seconds to parse starts taking 2+ minutes (or more) and that's when I know it won't be rendering fast enough. I had a scene yesterday start ok then when it started the third or fourth pass it would drop.

I don't often use CoronaAO or CoronaRoundedEdges. I prefer chamfered geometry over rounded edges but sometimes I use AO. The last few scenes though have not had either.

Corona benchmark was ok. I ran it several times and stopped/started several times to see if I could trigger anything but it was ok at 95-100% usage. Result attached.

It seems to cause the issue to come up more. It does inevitably start up again. I think scene complexity has something to do with it too. It's all very odd that this just started happening and I've never had issues before. I've had plenty extremely dense scenes with thousands of proxies, displacement, high res textures etc... and having to virtualize memory. Those scenes slow down to start but the CPU was never an issue. You think more ram would help?

Windows is up to date.

No power saving and is set to high performance.

I use default performance settings path tracer/UHD cache except now for turning off caustics solver.

Avi:
Thank you for your update.

Can you use this string option to turn off bucket rendering to see if it helps?

use this string code

"string option: int progressive.boxScramblingPassLimit = 10000"

You will need to put it in the string option that is present in the development/experiment stuff rollout in the performance tab of Corona render setup.

If the issue persists then please also try to turn off the adaptivity in development/experiment rollout section.

Remember, you will need to enable devel/debug mode by going into the system tab>system settings>enable devel/debug mode and then you will find a new development/experiment stuff rollout section in the performance tab.

Mirage Studio:
Hi Avi,

I get an error: Invalid string option: string option: int progressive.boxScramblingPassLimit = 10000

I just bought another 128gb of ram so see if that helps (I was past due for it anyways).

I was thinking more about the timing of this and I can't remember if this started happening after I upgraded from Corona 10 to 11. I'm going to downgrade back to 10 and see if that solves the issue too. I upgraded from 10 to 11 while I was still using 3dsmax 2021 and it happened both on 2021 and 2024.

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