2.79/2.80 Builds without dual render/hybrid GPU+CPU

Hi everyone,

does anyone know how to make a build without dual render please?

I’m on a laptop with Optimus (Discrete GC: Nvidia Geforce GT 640M and Integrated GC: Intel HD). And ever since the 2.79 builds came out with GPU+CPU rendering I have had a problem when running Blender. My problem is that with dual render builds, it seems that something is always soliciting the GPU and CPU even when I’m not doing anything in Blender and I can see the temperatures of my whole system (gpu and cpu) slowly but steadily increasing until my fans kick in and the temp stabilizes at around 57C (on a cool day).

I don’t have this issue/behavior with Blender 2.79b without Dual render, and the temp when doing nothing is around 45C. On a hot day I don’t use Blender because it simply makes my laptop too hot.

I know the GPU is always solicited by something because I can see it on the “Nvidia GPU activity monitor”. On 2.79b/ pre dual render builds, it only shows GPU activity when I’m really doing something with the GPU (basically when I render with it) and then it shows no GPU activity when the render is finished or I leave preview render.

With dual boot builds, as soon as I select “cycles” in the render engine list, or open the preference/system tab. The GPU starts being used and the fans go on, etc. and it doesn’t stop even if i go back to Blender render. I had to select Blender Render in the engine list and save the startup file that way to prevent this behavior.

You can see on the right the activity icon is on even though it says “none”.


I could keep using 2.79b, however I want the bevel node, the displacement node, the vector displacement and the AO node.

Does anyone know if a build exists without dual render (just with GPU as in 2.79b).

If not, does anyone know where in the code that could be disabled?

Thank you
kindest regards.

Have you tested 2.80?

AFAIK the latest build without GPU+CPU is 2.79b

1 Like

There is no option to disabled Cycles CPU + GPU rendering besides changing the preferences to select only the needed devices. However the issue you are having can not be caused by CPU + GPU rendering in itself, it must have been another change that happened around the same time.

If you are able to build Blender yourself, you can try to figure out the exact revision that caused the problem (manually or using git bisect).

Yes, I have tested Blender 2.8 and have the same issue. You are correct 2.79b is the last one without gpu+cpu and the problem doesn’t exist there. That’s why I linked the cause of the problem to gpu+cpu implementation.

Thank you

I don’t think it’s caused by the rendering itself but rather by the code detecting the available GPU and CPU. It seems as though it’s always “polling” or “querying” (for lack of a better word, I’m not a developer :)) the GPU. I researched and found this patch as being the one which introduced GPU+CPU:


I am trying to build Blender but I’m on a very slow internet connection (1mbps) and Visual Studio Community + Cuda drivers are a bear to download, with downloads failing multiple times already. But I will keep trying, it will just take time and as I’m not a programmer it will also take time to figure out how to remove the above mentioned patch.

Thank you

EDIT: I read Blender Runtime Libraries are about 6.5Gb, is that correct?

However the issue you are having can not be caused by CPU + GPU rendering in itself, it must have been another change that happened around the same time.

I was convinced it had something to do with GPU+CPU, but you may be right. After searching for older builds on my hard drive (I gave up trying to compile Blender myself as my slow internet speed gives me problems downloading all the required files), I came across a Blenderfracture build from 31 Oct 2018 (hash 3fa179f341220c8f41b40cae7dce523e647f532b) which doesn’t have GPU+CPU and it presents the same issue.

So the revision that caused the problem must have happened between 2.79b and this one.

I just realized that the 2.79b that I use and which doesn’t have the problem was 32bit, so I went and downloaded the 2.79b 64bit and it has the same issue. So you were right, it’s not the GPU+CPU render.

My system is 64bit though (Windows 8.1), so I don’t see what the problem could be.

It’s me again, I don’t know if you keep reading this :slight_smile: but anyways. After my last message where I explain that it’s the 64bit versions that have the problem. I went and downloaded Blender 2.79a and Blender 2.79 (from 2017) both 64bits and they both have the same issue. So the problem is confirmed to exist only with the 64bit versions.

Does anyone else have this issue (Optimus + 64bit Blender)?

EDIT: I have also downloaded 2.78 64bit and it also has the issue, except this time even when Blender render is selected, whereas with the others it starts when I select Cycles in the render engine menu.

I’m not immediately sure why this would happen. Perhaps whenever we use CUDA, even just querying the available devices, the NVIDIA graphics driver decides to go use the NVIDIA card instead of the Intel card, or goes into some performance mode.

There may be something in the NVIDIA settings to tweak this, but I’m not sure.

After some more tests, I downgraded my NVIDIA drivers to the last version published by the manufacturer in 2013 (Sony, Vaio laptop), and the issue was gone on 2.79b 64bit. But on any other build of 2.79 (like the last one of june ) I can’t render or preview, it crashes Blender with Error: EXCEPTION_ACCESS_VIOLATION, same with last 2.80.

So installed back the newer drivers (not from Sony but from Nvidia) and I’m back to square one.

EDIT: just as a reminder 32bit version work well with both drivers, it’s only the 64bit versions that creates the issue. But unfortunately cuda was dropped for 32bit.