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I have a Quad core CPU, that renders 4 chunks at a time. I also have a GTX 1060, which renders one chunk at a time, but renders chunks about 4x faster than the CPU. Can I use these both in the same instance of Blender for rendering? So I would be rendering 5 Chunks at a time. Or maybe the GPU would assist CPU somehow? I know you can just open blender twice and do skip framing, but I want something more convenient.

Note that I want to use this for rendering with Cycles.

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    $\begingroup$ Basically no, this cannot be done. You have to render in either the GPU or on the CPU. I can't claim to know the technical reason why the calculations cannot be split between them, however, I am sure someone will know. $\endgroup$ – Lewis Oct 14 '16 at 15:12
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    $\begingroup$ FYI they are usually called tiles or buckets, not chunks. $\endgroup$ – PGmath Oct 14 '16 at 15:26
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    $\begingroup$ Skip framing? Sound like a hassle. What I do: In 'output' turn off 'overwrite', turn on 'placeholders'. AFAIK, this works unless there's unbaked simulations. If I have more memory and the scene is not too bad, I'll start up more. (Because there's a gap of no cpu use between frames.) Often 2 or more running cpu, one gpu. (more gpu may be ok.) It doesn't mater if one instance of blender is faster. If a frame doesn't exist, it makes an empty place holder, then renders. (Tip: Make the output location a network shared folder, start up multiple machines for a cheap easy render farm.) $\endgroup$ – JTxt Oct 14 '16 at 16:44
  • $\begingroup$ Also be aware that using GPU and CPU for the same image might result in different qualities. This also might happen if you use different GPUs. $\endgroup$ – metaphor_set Oct 15 '16 at 0:30
  • $\begingroup$ Related: Cycles hybrid rendering $\endgroup$ – user1853 May 11 '18 at 0:06
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Kinda but it's not recommended. You could have 2 instances blender open and set one to cpu and the other to gpu. By turning on placeholder under the render tab you can in theory have both devices rendering the same scene at the same time.

Now the reason you don't want to do that is because the devices calculate and process the data in completely separate ways. This means you will end up with different images. Best thing is to stick to one or the other.

[UPDATE]

It's now possible to use both using the hybrid rendering option in 2.80 where, i believe, the render will fallback to system ram if you run out of vram for your render.

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  • $\begingroup$ Do you know if there has been any tests on to see if there's any tiny little changes between the two? I might test this later $\endgroup$ – Josh Silveous May 25 '17 at 17:53
  • $\begingroup$ I know there have been but I can't think where they are. Best thing would be, as you say, test yourself. It cold be that you don't notice a difference and are happy to try it all out. $\endgroup$ – Andrew May 26 '17 at 10:07
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It is now possible.

In the latest versions of 2.79 (check for the daily builds) you can use Hybrid mode: GPU and CPU as compute devices simultaneously.

enter image description here

Tile sizes have also been optimized for smaller tiles in GPU.

As always... test before you commit...

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  • $\begingroup$ wow! this feature is going to be so useful! $\endgroup$ – Joseph Farah Aug 3 '18 at 3:41
  • $\begingroup$ I can confirm this works in Blender 2.83.4 (lts). Using AMD Radeon VII and RYZEN 7 GPU. While rendering you can see the multicores in the RYZEN working on tiles while the Radeon VII chugs away one tile at a time at a much faster rate. It's really awesome to see this in real time! $\endgroup$ – C.Rogers Aug 8 '20 at 12:47
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I have an idea: split your image in two (region render; one upper half and one lower half). Open blender twice, render the top part of your image in CPU mode in the first instance of blender and render the the bottom part in GPU mode. Havent tried it yet but it should work. As an alternative you can ask (by using region render or for animation splitting the animation) ask friend (other blender enthusiasts) and family if you can use their PC (through teamviewer with a pre-set password) to use their PC to render those other parts of your image/animation partially on their pc. This I actually did in the past.

Region render: Render just part of a final image from Cycles?

Have fun!

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    $\begingroup$ When you post an answer you should take the time to try it yourself and post your results as well. $\endgroup$ – kheetor May 11 '18 at 10:13

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