Question about CPU vs. GPU Usage

DDCreate

I am using a Cyberpower PC Desktop with i7Core, GTX 960 4GB GPU, 24GB RAM and I render in IRay

My question is that no matter how many people are in my scene (normally 2, sometimes 3) my GPU kicks over to my CPU and runs at nearly 100%. I understand if it's a large or complex scene, a lot of people ect...that it will render slower but when it's just 2 people in a living room for instance, a few furniture props, a couple primative planes, a single Iray indoor light set and a 3point light set (maybe a few point lights for lamps) it still is too much. Are there some settings I can change to sort of make my GPU pull it's weight? From what I've read here, I think i am working inside my GPU capacity but it's sending my CPU almost through the roof. Any advice would be much appreciated.

 

jestmart

It is the textures on the models not necessarily the number of models.  Most of the textures for the last few years are 4K, multiple that by the number of texture and you see why the GPU would run out of memory.

Tottallou

If you have both CPU & GPU checked in your render settings it will use both to render making CPU run at around 100% so you could try unchecking CPU as I find including it does not save any time of course if you are exceeding your 4GB GPU limit that won't help at all - Reducing Texture sizes as jestmart mentions saves a lot of GPU memory & you probably don't need 4k textures in a scene with several characters

 

 

 

 

Richard Haseltine

How much sub-division is being applied to the mdoels? If the items have a high Render SubD level (in Parameters) or Displacement SubD (in Surfaces) then that can push up the memory use to the point where a single item will overwhelm the RAM - the surface setting in particular can be a killer, I had a piece of clothing with the Displacement SubD set to 5 that was enough to break the bounds on a bald figure.

DDCreate

Thank you everyone. I did 2 renders in a blank scene with just my character in her outfit. One with CPU/GPU and one with just GPU and they rendered in about the same time and quality. We'll see what happens on a full scene.

Richard, good tip on the SubD levels. I'm going to load my scene and see who the culprit might be. My character read a 2 in render and her outfit was 1 in both other categories. I do have a big mirror in the scene. Wonder if that's it. But thanks for the tip!

Richard Haseltine

The setting in the parameters pane is a minimum - it can be overridden, as it was in my case, by the setting on the surfaces (the maximum value across all surfaces applies to the whole model, even if only one part has a higher value - the zip material for the item I was using). Apparently the code that handles the shader-level division for SubD can cause bigger memory spikes than the object-level setting in the Parameters pane, which may be hard to spot (in my case GPU-Z showed at least 1GB of RAM clear right up to the point where the GPU was dropped).