CPU Throttling Down During VRay Rendering

[hrigsby]

Hey everyone:

My issue is that when I start rendering, my CPU is throttling up to 100% but then probably 75% of the time it will drop back down to utilizing one core almost instantly. When I watch my Task Manager I can tell what's happening. Essentially, VRay isn't utilizing all of the RAM that my system has available and it starts using my disk, which slows everything down. The solution has been to go into Render Setup -> Settings -> System and mess around there by changing the Dynamic Memory Limit and clicking Embree off and back on again.

Eventually, this will work and VRay will use all of the RAM that it needs to keep my CPU at 100% throughout the render (I have 64 GB and I've never gotten about the 50% usage mark while rendering). The confusing part is that I can finish that rendering, click render on a new one in the same file without changing any settings, and it will throttle down again as it did before. The only solution is, again, to fiddle with the Dynamic Memory and restart the render a few times until it works.

I've tried setting the limit to 0 so that it uses what it needs and I've also tried setting it very high (48000, 50000, or 64000) and none of them work consistently. Any ideas as to what the problem is?

My system is:

- i7 6900k
- 64 GB RAM
- GTX 1070

It's definitely doing this on Buckets but I'm about to check to see if it does the same during progressive.

Thanks in advance for any help you can offer!

[Schellicon]

is this scene dependant?
sounds for me like:
check your cpu cooler , those new cpus slowdown to prevent overheating.
(but if the hdd starts swapping sounds strange)

[hrigsby]

is this scene dependant?
sounds for me like:
check your cpu cooler , those new cpus slowdown to prevent overheating.
(but if the hdd starts swapping sounds strange)

It could potentially be scene dependent. I was messing around with a really simple scene earlier and it didn't do this. It also hasn't yet done it in Progressive mode today.

I won't say that it can't be the computer controlling temps, but I am 99% sure that isn't the case. I'm a habitual monitor of my hardware and I've never gotten about 70 C while rendering. That, coupled with the fact that it's doing it so quickly when the rendering starts, leads me to believe this isn't the issue. The only way it could be is if the sudden surge in temp is causing it to preemptively throttle.

[hrigsby]

As an update, the CPU acts the same whether I'm set to Buckets or Progressive. I'm still unsure of the file dependency.

[yavor.rubenov]

Hello,

Could you then send one such scene to our support?

Best regards,
Yavor

[hrigsby]

Hello,

Could you then send one such scene to our support?

Best regards,
Yavor

Sure thing, I just emailed a link to it over.

VRay Version: VRay Advanced 3.50.04
Modeling Software: 3ds Max 2017
OS: Windows 10 Pro x64

[vraypixel]

Hi Guys, I have a similar experiance with my Ryzen 1700 only I can literally see the clockspeed drop. Default on my hardware Ryzen 1700 works on 3.2 Ghz on all cores. This remains so in Corona benchmark, Cinebench, Prime etc with all cores maxed out to 100%. But as soon as I use Vray progressive or bucket mode, Vray benchmark, light scene, heavy scene anything, the clock speed drops just and oscilates around 3Ghz (2997-3095MHZ). Temperature is 100% not an issue as the cpu gets far hotter with prime95 for example while maintaining the maximum clock for all cores 3.194 MHZ to be exact. If I use OC and fix the multiplier rate to 3.2 for example than the drop doesnt happen. Oh and btw I'' working on a Win10 x64 Pro machine with 64GB of RAM and Vray version 3.5.03 and have also updated since to 3.6.03 and the same thing happens.

[vlado]

Use the Ryzen Master application to fix the clock speed of the cores. We have not found the precise reason yet and the AMD guys are ignoring the issue, but it seems like the power efficiency logic of the CPU gets confused. From my tests, this leads to about 5% performance loss on the total render time, so it's not that big a deal.

Best regards,
Vlado

[vraypixel]

Ok Vlado, Thank you for the reply. I was going crazy about the reason why this happens but I'm glad that at least its a known issue. I have noticed that the downclock becomes much less or dissapears If i turn Embree off. You can try to replicate this if time allows and I would be happy to hear about any conclusions that can be drawn from it.
Best regards

[vlado]

I have noticed that the downclock becomes much less or dissapears If i turn Embree off. You can try to replicate this if time allows and I would be happy to hear about any conclusions that can be drawn from it.

Hm, that's interesting, will check it out. We recently updated to a newer version of Embree, I have to check if it changes anything. In any case, rendering with Embree is way faster, even with this problem.

Best regards,
Vlado