Cpu not running 100%

[philip_nel]

Hi there, I've asked this question on the Creative Lighting Masterclass and Nikos suggested asking it here:
When rendering scenes, cpu would run a few minutes at 80-90% with buckets rendering as it should (Ryzen 5900 12 cores)
But then it would drop down to 5-12% and the buckets won't move for a minute or so.
Then it would jump back up to 80% + and render again.
What would cause this, is it a memory issue (64Gb installed)? Or is it geometry loading in every few minutes?

Any vray/windows settings that can be adjusted?
Please advise...

[philip_nel]

Thanks for the feedback guys.

Think the issue is sorted now - I hope:

Ryzen Master App indicated high cpu temp (70 - 80 degrees, limit is 90 degrees) and wattage (100W+ of 142W) when rendering.
CPU cores also didn't render at full 100% but rather a bit over or under 90%. Individual core graphs were always moving slightly to the left/right.
And then all the cores would drop to 5 or 10% for about 90 seconds and buckets would stop rendering.

This happend with default bios settings.

Then I started to adjust the Voltage control (default 1.387V) - undervolting, so lowered it by small amounts.

CPU temp came down to 50-60 degrees and CPU power to just over 60W.
Now all the graphs are in mid green levels except the EDC (CPU) graph which runs at 100% of 140A - is this normal?

But most importantly, the cores are all running at full speed with no small variations or dips!

Not sure if this is a specific issue with the Ryzen 9 5900X 12-Core processors or just my pc that's "special"...

[Joelaff]

If your machine is thrashing (swapping out to disk because you don't have enough RAM) it might do something like that. Also, sometimes Progressive seems to do this, but the bucket renderer is typically pretty good at keep the processors saturated during rendering.

You can check your memory usage in task manager and see if you are running out of memory.

[vladimir_krastev]

Hi, thanks for posting. First step is to make sure you are not exceeding the RAM capacity on you PC as Joelaff said. Please monitor your memory consumption during rendering to make sure you have enough RAM. Once you are certain you have enough memory please run a few tests to see if you are getting these issues in every scene and let us know how it goes.

[philip_nel]

Morning guys, thanks for the reponses.

I'm not running out of memory - I checked the task manager throughout the rendering - never used more than 62% memory.
Image would render around 3 min and then the cpu's will drop for 1.30 min.
This happenend 4 times during a 30 min render which means 6 minutes of nothing happening.

With enough memory the windows page file shouldn't even come in to play? I've also increase the page file size for in case - Windows 11.
It's a smallish interior scene with gym equipment - no vray proxies, just groups.
File size is around 2GB though - but easy to navigate and IPR also quick.

Really frustrating.

See attached images for more info.

[vladimir_krastev]

With enough memory the windows page file shouldn't even come in to play?

You shouldn't rely on swapping memory to the hard drive. This can cause exactly the effect you are describing and should be used only as a last resort in case of emergency. With 62% of the memory in use, the issue is somewhere else.
There could be something in the scene that is causing an issue. Is this issue happening in every scene or only in this one?
Please make sure your PC is running with stable performance during long periods of 100% load. Try the V-Ray Benchmark Tool and any other stress test for testing CPU performance.
Also you could test this with a new simple scene (a box and a light) but make sure it renders for longer periods. For example render it at a high resolution and high image sampler settings (low noise threshold and high max subdivs)
If your system runs ok with other tests but not with your scene there could be something in the scene and we will have to review it.

[philip_nel]

Thanks Vladimir - just did a test render on a simple scene - basic room with tree in the middle.
Memory usage 50%

Same thing happenend - cpu's drops down after a few minutes and render buckets stops until cpu's pick up again.

Also ran the Vray benchmark tool - happened twice in a 10 min test, same issue.

Maybe a hardware issue then?

[vladimir_krastev]

Hi, if VRayBenchmark is doing the same it most probably is something outside rendering that is causing the issue. It won't hurt if you uninstall V-Ray and install it again if you haven't done that already.
Are you using the latest version of V-Ray and what is your 3ds Max version?
Please make sure your CPU is not overheating and your operating system is not limiting it's power for energy savings. Check your windows power settings carefully.

[philip_nel]

Thanks for the response Vladimir.

Vray 6, update 2.1 (think that's the latest version) with 3dsmax 2024.
Cpu temp looks fine - checked it with the Ryzen Master app.

Will check the power settings.

Edit: I checked power settings and installed Vray again.
CPU temp at 78-80 degrees C when running at 100%. Then it goes down to 53 degrees C when CPU power drops to 10%.

[vladimir_krastev]

Hi, please try a dedicated CPU performance test like for example this one. Do that at your own risk.
If the CPU stays at 100% during extended testing please return to the thread. If the same drop happens the issue is most probably outside V-Ray.
Please turn everything off during every test since if you are not something might interfere with the result.

[Joelaff]

Also try a full shutdown/ power off the power supply switch. We have a threadripper 5000 series that has needed that to fix a low cpu usage issue (~80%). Worth a test.

[philip_nel]

Thanks for the feedback guys.

Think the issue is sorted now - I hope:

Ryzen Master App indicated high cpu temp (70 - 80 degrees, limit is 90 degrees) and wattage (100W+ of 142W) when rendering.
CPU cores also didn't render at full 100% but rather a bit over or under 90%. Individual core graphs were always moving slightly to the left/right.
And then all the cores would drop to 5 or 10% for about 90 seconds and buckets would stop rendering.

This happend with default bios settings.

Then I started to adjust the Voltage control (default 1.387V) - undervolting, so lowered it by small amounts.

CPU temp came down to 50-60 degrees and CPU power to just over 60W.
Now all the graphs are in mid green levels except the EDC (CPU) graph which runs at 100% of 140A - is this normal?

But most importantly, the cores are all running at full speed with no small variations or dips!

Not sure if this is a specific issue with the Ryzen 9 5900X 12-Core processors or just my pc that's "special"...

[vladimir_krastev]

Hi, thanks for investigating and sharing the information. We have had similar cases with Intel i9 13900K and 14900K. Undervolting and other BIOS tweaks have helped others with the Intels as well.