CPU / GPU / Render Etc

Hi folks.

Right. I’ll try to be as concise as I can be while not knowing much about my topic! (Please assume everything is Blender related)

I may well soon be, in the very privileged situation, of being able to buy a new setup.

Now, I’ve watched my task manager with interest while testing loads and loads of different rendering options. -At the moment, for all the difference it makes, I’m not going to use cycles, it’s horrifically slow and well beyond my brain power to work out.- Blender Render with loads of lighting and lots of pollys jumps up and down the CPU usage, but typically only uses 20%-50% of my processing power (4 cores + virtual) and no more than 3 out of the 16 Gb I have installed. I have to say at this point there are no textures involved which I know will make a big difference to time performance.

But, what I’m really confused with is the usage of the GPU. With Cycles my CPU is hammered to 100% while rendering an image and it takes 3 times as long to render a simple scene. (I mean very simple) Isn’t the idea of utilizing a GPU meant to speed things up? And I get getter results with B.R.

I remind you of my second paragraph, I don’t know how this stuff works!

Now for the bit that matters…

I have to work and render on the same machine, I can’t afford a farm. Should I look for a multi processor machine, or go the SLI route with a half decent setup? This wont be a games machine, it will only run graphics stuff.

(I currently have an i7 37xx full 64bit, nV GTX 670, 16Gb, SSD OS, 1 Tb data drive) Oh, and a mouse!

Any advice would be very much appreciated. Experience, what you use any why, what you wish you’d bought, etc. I look at some of the work on here and my mind boggles, there is no way my system could handle anything close.


and no more than 3 out of the 16 Gb I have installed.
It will only use as much as it needs

I’m not going to use cycles,…or go the SLI route with a half decent setup?
The Blender Renderer does not use the gpu so you won’t speed up rendering with a hefty gpu or using SLI

For The Blender Renderer is uses your processor cores to render multiple tiles so the more the better as long as you have set to use the maximum number of threads in the render settings. Adjusting the tile size can change render times, you want all the threads working all the time. There are some hints about rendering performance in the blender manual (link in blender help menu) under ‘Rendering with Blender Internal’

Thanks for your reply.

Yes, I understand the settings, all cores and virtuals are being used correctly.

What I don’t understand is, if Cycles uses the GPU, why is my CPU hammered using it. When B.R. doesn’t hit the CPU half as much, and is quicker.

you have to go into the user preferences and look under the system tab and tell it to use the GPU
it can use either the CPU or the GPU and I think it defaults to the former

Found part of the problem. I’d set the GPU in the user prefs, but hadn’t spotted the extra setting in the Render panel where you have to set the GPU again. Not quite sure why you should have to make the setting twice, but it has helped dramatically.

Thanks for your help.

Not quite sure why you should have to make the setting twice,

Some systems have more than one GPU so you have to choose.

No, I only have the one.

So, I’m guessing an SLI setup will improve cycles render times?

the cycles render engine uses CUDA for computation. SLI from nvidia is only beneficial in terms of speeding things up for games or viewport display. you will NOT get ANY benefits if you connect two or more cards in SLI. in some cases I think it is actually slower.

best is one card for display and one for GPU computation only.