Threadripper CPU clock speed and Vray

[DPS]

If I set windows 10 power management to performance then my CPU idles at 3.7GHz.

But when I use Vray the clock speed drops to:

1) around 3.45GHz full load (with XMP profile enabled in the BIOS i.e RAM overclocked to a 2933MHz)
2) around 3.57GHz full load (With XMP diabled i.e running RAM at native 2133MHz)

If I try chaosbench the clock speed sits around 3.48GHz

When I first build the machine I had all cores maxing out at 3.7GHz whilst rendering.

This is all without any manual overclocking apart from enabling the RAM XMP profile. CPU temps are around 55 deg.

Any ideas why this is the case?

[vlado]

I've noticed it on my Ryzen 7 machine, but I don't know why that is. My guess is that the CPU's power management gets confused by V-Ray's code for some reason. I flagged the issue to guys at AMD last year, but I didn't get a reply.

I ended up using RyzenMaster to peg the CPU frequency to 3.7 GHz. The eventual difference in rendering performance is only about ~5% anyways.

Btw is there any difference between V-Ray 3.6 and V-Ray Next?

Best regards,
Vlado

[DPS]

Well that was easy - thanks. Shaved a couple of secs off the benchmark, it's not a lot extra but may as well use it.

[DPS]

Also I?ve not tried VRay Next yet.

And i I had a reply from AMD - they suggested to disable Cool and Quiet in the BIOS.

Not tried this though as your solution works.

[DPS]

The reason for the lower clock speed when using Vray is because there is a power saving feature built into the processor - so the clock speed drops when it is consuming more than 180W.

Vray with all cores at 3.4GHz = 178W ish
Vray with all cores at 3.7GHz - 192W ish

Ryzen Master disables the power saving/heat feature.

[urbanite]

DPS, what temperatures do you get when it is set to 3.7GHz?

[DPS]

One runs at 52degrees (tdie) - this one is sat under the air conditioner and has a larger case.
The other, my workstation, runs 56- 58 degrees - but from 57degrees it appears to start automatically lowering the clock speed.

[urbanite]

Thank you DPS. Mine now is 3.3GHz and 67 degrees accordingly to Ryzen Master. When it is set up to 3.7 temps goes almost to 90 (cooling NZXT Kraken X52) . I have red that the cpu would shut down in emergency but I would not want to try or see it. I would guess that the sweet spot would be around 3.5 fixed.

[DPS]

I?m assuming those aren?t the tdie temps (ie the real ones)?There?s a 27 degree offset on your temps. So you?re running between 40 and 63.

[urbanite]

Well, those are temps that ryzen master is showing me. I have red about some temp offset that needed to be taken into account with new amd processor but I do not know if this is the case with RM.