OT: Tech discussion understanding GPU

AJ2112

The confusion I have is cpu vs gpu.  After tons of research, I still don't understand gpu for 3D rendering.  Reason being from my experience, with each GPU upgrade, I never noticed any significant difference in rendering speeds, but I do notice increased speeds in Iray preview, such as going from GTX720 to 1080, but not rendering.  

When I open task manager during render, my comp cpu/memory is used more then gpu ????? and cpu is unchecked.  My gpu% never goes above 4%, but comp memory goes way up 50, 60, 70%

Which leads me to believe, comp cpu/memory is more vital then gpu.  Or my gpu is not calibrated for rendering.  

I read an article that best cpu on market for 3D rendering is AMD 16, 24, 32, 64 cores.  Would appreciate if anyone with these cpu's can provide feedback.  I was thinking of upgrading to 16 core. 

If graphics cards is of great importance, then how come rendering always falls back on cpu/memory ?

Does the gpu actually do the rendering or cpu/memory ?  According to my task manager, it's not gpu.  

I'm not very tech savy, but from I'm understanding is, gpu has to have more memory then comp system, to render gpu.  Example, if comp is 16GB ram and Vram is 8GB,.  Vram has to be higher then 16GB, not to fall back on system memory.  So until Vram is higher then comp memory, 16GB, 24GB, 32GB, 64GB, card will always fall back on system memory.

Sorry for writing book, I don't understand the importance of expensive graphics cards for 3D rendering, gaming yes, 3D no.  Thanks.

Richard Haseltine

Task Manager does not, by default, account for CUDA activity - if you go to the performance tab and for GPU set one of the graphs to CUDA (or Compute_) if CUDA isn't there) you should see the actual activity if the GPU is being used.

AMD GPUs will do nothing fro Iray as they don't have CUDA (an AMD GPU will be used for dForce).

The render will fall back to CPU if the GPU runs out of memory, which is a function of scene complexity. The system RAM is generally said to need to be about twice the GPU RAM, remember that the scene in DS is different from the data sent to the GPU (that gets higher resolution mesh and textures, but doesn't need all the rigging information) so theer needs to be enough space to both handle the scene and prepare the data for the GPU. Do note that non-RTX cards, such as the GTX 720 or 1080, get extra code passed to them to implement the features (if not the speed) of the RTX cores, so you are effectively more limited with memory on those than on newer RTX cards.

AJ2112

Hi Richard, thanks for the info, will check out in a bit.  AMD cpu not gpu.  Gotcha, thanks.  So, I need to learn process how scene and rendering differs.  So, that's what I'm trying to understand, what is the purpose of upgrading graphics cards every year ? If only minute changes are made.  Technology does not make any sense to me at all.  One side is always catching up with the other, vice versa. 

Why purchase a 4K HDtv or monitor if techonolgy around it has not caught up ? 4K was introduced in 2014, 6 years later game consoles introduce 4K gaming console.  4K blu ray players are mainly upscaled.  

So, makes me wonder about graphics cards.  Graphics cards are mainly designed for gaming not 3D rendering.  All the specs for graphics cards are game specific.  So, cpu/memory software rendering is preferable. 

Anyone know what specs are specific to 3D rendering ? other then Vram ?  So, the clueless will know what to upgrade in the future, if it's worth or not etc....  From what I've been reading Titan cards are still best choice, but expensive.   

Thanks    

jmtbank

There is a tiny easy to miss gpu and cpu tick box on a side panel under the render settings pane (where you change the shutter speed and turn on bloom etc). Right at the top on a sub tab.  Guessing you may not not have gpu ticked.

The 1080 should render far quicker than cpu.   You should notice its fans spool up slightly when its rendering.  Not quite as hard as gaming though. 

Windows task manager often won't acknowledge Iray activity.   Most people use gpuz. Even Microsoft seem to suggest it. 

https://blogs.windows.com/windowsexperience/2013/08/01/monitor-your-gpu-on-windows-with-gpu-z-by-techpowerup

TheKD

The more and the newer cuda cores, the faster the render will go.

Havos

As jmtbank says, I would advise that you download and install GPU-Z.

This will report what percentage of the GPU is being used as you are rendering, and if that number is not close to 100% then something is wrong with your set-up.

If the GPU is not being used, even for a simple scene with few assets, then the first thing to check is that your GPU drivers are fully up to date.

AJ2112

Hi jmtbank, thanks for info, all I see is render settings > advanced tab to select cpu/gpu. 

GpuZ shows graphics card working.  Wow ! just a nude base figure/hair, 1080 resolution, Gpu load 100%, memory used 4.6 GB, rendered 7m 20 sec.  That's half my gpu memory.  Without hair 4.4 GB, but rendered 1m 34 sec, 

In Iray preview 1 view pane, 4K 43" monitor hair/no hair. same information.  Iray previews clears fast with hair. 

Task manager memory 50% stable, gpu memory controller bounces around 31%-50%  Interesting......

jmtbank

You got it! :D

Sounds like everything is working normally. 

nicstt

For anyone coming across this:

Do NOT compare CUDA cores between generations. 1000 cuda cores from the 3000 series are not the same as 1000 from the 2000 series as an example.

 

cajhin

for a final "Aha!" you could render your 7 minute scene on CPU and look at your 1h+ render times.

My quick check is to view CPU load during rendering in task manager. If all cores are at 100% all the time, it's CPU rendering; otherwise GPU.

And new cards really make a difference. A 3080 would probably render your scene in a minute. (unfortunately... my 2070 is just 4 months old, but as soon as a 3070 16GB shows up I'll be another 500 poorer)

AJ2112

cajhin said:

for a final "Aha!" you could render your 7 minute scene on CPU and look at your 1h+ render times.

My quick check is to view CPU load during rendering in task manager. If all cores are at 100% all the time, it's CPU rendering; otherwise GPU.

And new cards really make a difference. A 3080 would probably render your scene in a minute. (unfortunately... my 2070 is just 4 months old, but as soon as a 3070 16GB shows up I'll be another 500 poorer)

Thanks Cajhin, I've never had any issues with products using DS, products work fine, satisfying render speeds.  I began questioning the integrity of my comp/gpu with Post Apocolyptic Zone.  Your not alone friend, enjoy new graphics card.  I'm awaiting the 3000 series cards to be available and compatible with DS, which would be a major boost over my GTX 1080 FTW    

AJ2112

jmtbank said:

You got it! :D

Sounds like everything is working normally. 

Yes, very much so, thank you friend.  Now, I can't keep my eyes off GPU-Z, Rofl !!!