Render with CPU and GPU simultanously

Hi. Is it ok to render with Gpu and Cpu simultanously on the same machine with blender?
tks:D

Since the GPU is reliant on the CPU to provide it with instructions, there would be no speed gain (and in fact there’d probably be a speed penalty) because the GPU is competing for CPU cycles.

You absolutely can with the caveat that what tjdolphin says is correct in some GPU configurations and/or for some scenes. I’ve done concurrent CPU & GPU rendering and sometimes had good results, sometimes poor… totally depended on the scene. The main thing to look at is: how busy is your CPU when doing GPU rendering? If you see one or more cores (I’ve seen two cores maxed out in some cases: one for Blender, one for the OpenGL/CUDA driver) maxed out, you will probably not have a great experience also trying to render on the CPU. However, if the CPU utilization is low, definitely look at rendering on both. Also, if you do, be sure to make sure the rendering priority on the CPU rendering instance of Blender is lower than the GPU rendering instance to make sure you keep the GPU fed.

Oh yeah, one thing I didn’t consider was the multicore aspect. My bad.

Easiest way I’ve found is to set your GPU to render frames 1-200, and your CPU 201-250 (varies of course by scene length and CPU/GPU count/power), using 2 instances of Blender. This assumes enough system ram.

To ensure your GPU’s don’t get slowed by the CPU being in use, I look at how much CPU is being used when rendering. My CPU is a 4 Core, 8 Thread i7 4790k

With 1 GPU (970) in use, I get ~14% CPU usage. With 2 GPU’s (2x 970) I get 28% CPU use. So basically 1 thread per GPU.
So I render with 6 Threads in Blender (CPU), and for good measure reduce the priority of the CPU render as well.

Hi zeealpal.
I do not really know much about animation, but I’m interested in that method. Do you know what must be taken into account to prevent inconsistencies between what CPU and GPU render? If there are physical simulations for example, in the part of the CPU (201-250), I guess the simulation must be baked, but I’m not sure really and I don’t know how Blender works when it starts to render from a frame that is not the starting.

Yafu,

When I render, I’ve always baked the things beforehand on the same machine (which I’m rendering on). So I just open the same .blend file twice, adjust the settings for CPU/GPU and then get it to render. They should both be using the same cache(s) etc…