Page MenuHome

Cycles CUDA+CPU results in different random output per rendering tile
Open, Confirmed, MediumPublic


System Information
Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: Quadro M4000/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 411.63

Blender Version
Broken: version: 2.82 (sub 3), branch: master, commit date: 2019-11-30 17:33, hash: rBf1ac64921b49
Worked: (optional)

Short description of error
Cycles appear to produce different random values for CUDA tiles and CPU tiles.

Exact steps for others to reproduce the error

and compare rendered view with rendered output.
Images of the bug in isolation.
CPU Only - Fine:

CUDA Only - Fine:

CPU + CUDA - Bugs out:

In addition, I had some even more strange artefacts in a real render.
The random effect is more subtle here, but it's there. But the other ones I can't really reproduce, not sure what is going on with that:

I can't update drivers, due to other software requiring certain certified drivers. Windows 10 is up to date.



Event Timeline

Germano Cavalcante (mano-wii) lowered the priority of this task from Needs Triage by Developer to Confirmed, High.Wed, Dec 4, 4:19 PM

It is also possible to reproduce the problem with OpenCL
I was able to reduce the material to this simple setup:

The file simplified:

Just to tidy things up... can somebody confirn, that the bug I have documented in T69535: CPU + GPU render precision differences for small, far away area light is the same one like this here? At least it looks pretty similar to me.

It is very similar, I will merge here to keep as a reference.
If when this is resolved, any of the other reports are not fixed, they will be reopened.

So far the similar reports are: T69535, T70501 and T70712

Brecht Van Lommel (brecht) lowered the priority of this task from Confirmed, High to Confirmed, Medium.Fri, Dec 6, 7:32 PM