A VRAM oddity

Second Technician Rimmer

I created a scene for rendering which, when I loaded it and rendered it on my gtx970 (4.xGB of Vram), gave me a reading of close 4.00 gb of vram used.

I then passed the same scene, repackaged thanks to a script, to a friend who owns a gtx 1070TI (8GB of VRAM) and he rendered it. His reading was... almost 8GB of Vram used.

Shouldn't the same scene, using the same textures and settings in every regard, use the same amount of vram on both video boards?

Richard Haseltine

How were you getting the usage figures? Whereever it was, were you subtracting the before rendering value from the during value to make sure it was just the amount used for rendering that was being measured? Did you friend have another render window left open?

fastbike1

@second.technician.rimmer_9571136c47

Did you check that the texture compression settings are the same? They are sort of a hidden parameter that users typically set once then forget.

Another question would be how your friend was getting the Vram info? All users are not equially versed in obtaining/understanding the info. 

ebergerly

There's a bunch of reasons why that might happen, including:

• Are you sure in both cases your GPU's were actually doing the render, and they didn't crash to CPU? It's possible one or both scenes filled the GPU's VRAM until it ran out, then dumped to CPU to render, leaving the impression one took more than the other. In fact maybe it required more than 8GB and overloaded both GPU's. The fact that you say it used virtually all of each GPU's VRAM sends up a red flag.
• How are you measuring the VRAM usage of Studio/Iray when rendering the scene? There could have been other apps using the GPU VRAM on the different machines, giving the false impression that Studio was using it all. You can use the Windows 10 Task Manager to monitor VRAM usage of specific apps. Maybe your friend's machine was running a game or something in the background? 

Second Technician Rimmer

We both used GPU-Z to track how much vram gets busy in the end.What we were measuring was how much vram was used overal, including

prerender and after the textures got loaded. His DS is kinda "out of the box". He didn't touch the compression settings and neither did I on my side. 

From what I could see, his vram use was around 200MB before he started the render and once the xture loaded up, it jumped immediately at 7.5GB.

Actually, regarding the used Vram, is there even a way to have DS free some of it once a render is finished or even interrupted? :)

Richard Haseltine

As long as the render manages to stay on the GPU closing the render window will free up the memory, more or less. If the render runs out of RAM and drops to CPU then you will at least have to close and restart DS and may need to restart the OS.

Second Technician Rimmer

I see... I didn't know the render could just "drop out" of vram and go for CPU on its own. I more or less expected the whole thing to crash if the vram was overwhelmend while my settings were on GPU only. That's interesting, thank you  all for your guidance :)