I can not confirm this issue on MacPro with dual D700 GPU. 2.78c gives render time of 11min 30sec and 2.79rc1 gives render time of 11min 5sec.

@Brecht Van Lommel (brecht), @Arto Kitula (akitula), do you have access to mac with AMD GPUs?

I don't have a Mac with AMD GPU. It's quite strange that CPU render time would have doubled as well. GPU performance can be sensitive to all kinds of things, but for CPU such a regression is less likely.

Are you absolutely sure you tested under the same circumstances, no other heavy computation running at the same time, rendering the same exact .blend file? Are you rendering the files from the official benchmark unmodified? Is the 2.79 RC downloaded from the blender.org download page or a daily build from builder.blender.org?

I know it's really strange...
I tried both the 2.79 RC and the daily build from last Friday I think. It worked fine with the daily build for 2.79 before the RC came.
The reason I tried the benchmark file again was that I felt that my render times had sloved down, so I used it to check. I downloaded it from here: https://www.blender.org/download/demo-files/

I rarely use the GPU on my mac for rendering since the CPU is faster. Although I would like to be able to take advantage of my GPU.

Oh wait, so regression is about CPU? You mentioned bmw27_gpu, so i thought it's GPU render...

Try the following:

• get bmw27_cpu from the archive linked by Brecht
• Start Blender from command line interface, passing --factory-startup argument
• Try rendering and see if it goes faster

It's mainly the CPU since that's what I use. But the GPU is much slower too. Although it says in the release notes that OpenCL support for AMD cards is updated and that the GPU should be faster...
I will try these steps and get back!

The problem still remains even though I followed your steps Sergey.

Does your activity monitor show that there is all cores working at 100%? 8 tiles rendering every time?

Yes, all 8 tiles are rendering. But I haven't tried with the activity monitor open.
I'm rendering remote right now, since Im not at the office, I don't know if it affects the render time. But I tried rendering on 2.78c again (CPU) and very long rendering time. around 8 minutes... Maybe it has something to do with the new version of Mac OS?
I just think it's very strange that my render time more than doubled. Makes it kind of hard to work with...

I will have to do the tests again when Im back at the computer

Okay, back at the office so I did some new tests today.
2.78c on CPU: 07:22
2.79 RC on CPU: 07:59

Compared to the test I did a couple of weeks ago on 2.78c: 02:34

It seems that the blender version might not have affected the render time too much. But I wonder if it might be the newer version of OsX that slows it down? Either way it's very frustrating to loose this much time... It's also weird that I got 05:51 on 2.79 RC last week.

Is there a way to identify what's going on?

Did you check the activity monitor? Are all cores being rendering at 100%, are there any other applications slowing things down? Did you try rebooting the computer?

I used the activity monitor and blender is using around 775% i guess thats close to 100% on all 8 cores?

Here are the cores...

Hi.
For "bmw27_cpu.blend" scene downloaded from blender.org (not the BMW27.blend scene belonging to Blenderartists forum), the time you get 2 m 32 s looks to me very little time for an 8-threads i7 CPU. 5 m 51 s looks to me more feasible. What is the exact model of the CPU? Did you compare side by side the resulting images to see if they look the same?

hmm, I can't be sure actually since I didn't save the result. And I can't be sure if I used the other benchmark file earlier. It actually seems that this could be the case.

In T52395#452681, @Jonatan (jonhed) wrote:

And I can't be sure if I used the other benchmark file earlier. It actually seems that this could be the case.

If I had to bet, I'd bet that's what happened. Confusion between BMW blender.org and blenderartists forum scenes occur all the time.

So, you confirm if everything is working well using the appropriate scene so developers can close this report (or not).

I think you can close the report because it doesn't seem to have anything to do with the new blender version anyway.. :)
thanks for all your responses!