Cycles 2.79 vs 2.8 (2.79 much faster)

The same file, opened / rendered in 2.8
and opened / rendered in 2.79

First test was with slightly different settings, HDRi map was rotated to 90 degrees, and image size was 5000x5000
All shaders are procedural with translucent etc.

After that I just opened the same file in both blenders, decrease image size to 3000x3000 to reduce render time:

2.79 - 12m 20sec
2.8 - 17m 56sec

Did you set GPU and tile sizes same for both versions?

My selfquote is special for you :wink:

No, I didn’t change anything. Just opened my file in both blenders, saved it in different paths (2.8 folder and 2.79 folder to separate versions) and hit “render”.
GPU settings in preferences are the same.
In 2.8 CPU compute is switched off, only GPU.

Opening same file in both Blender doesn’t mean they have identical settings. Defaults of Blender 2.80 is quite different than 2.79.

No. Render settings are saved in the file.
If he had forgotten to precise GPU compute device in 2.80, rendertime difference would have been higher.

There are differences between Cycles in 2.79 and Cycles in 2.80.
It is logical to obtain different rendertimes.

What is expected from these changes and fixes is that they provide some good.
In 2.80, opensubdiv lib used is not same as in 2.79.
Problem may be related to use of displacement in .blend file.

But that may be something else.
Try to investigate a little bit what has changed in 2.80 compared to 2.79 and that your scene is using.
Then, when you will be able to replicate problem with simplest .blend file possible : fill a bugreport.

are we comparing the last official 2.79b vs 2.8, or a 2.79 nightly vs a 2.8 nightly?

Hmm, weird. I remember tile sizes were different when I opened a 2.79 file in 2.80 a month ago. Maybe it was a bug at that time, so I’m not sure.