Confusing GPU readings in Iray

Peter Wade

I've got a moderate spec computer with a 1050 ti graphics card. I use a utility called GPU-Z to see if Iray is rendering on the GPU. I've always assumed that if the GPU load goes up to 100% and stays there during the render then Iray is using the GPU. Sometimes Iray will stop using the GPU but stopping and re-starting Daz Studio will get it going again with the same scene. But recently I've seen something that puzzles me.

I had a scene with 2 G8 females, hair, clothes an some scenery. GPU-Z showed the GPU load between 98-100% during the render, memory used was close to the card's capacity but after 8 minutes convergence was still 0% and the image was very grainy. I stopped Daz Studio, restarted and reloaded the same scene with no changes. Rendering this again, GPU-Z  showed the same readings but after 8 minues the convergence was 28% and the image was a lot better than the first attempt. The render finished after about 45 minutes.

I wasn't running any other applications so I assume the GPU load was coming from Daz Studio, What was hapenning in the first render? Was Iray running the GPU at 100% but not getting any benefit from it? Is there a more reliable method for monitoring Iray's GPU use?

PerttiA

According to the pages I found, 1050ti has only 4GB's of VRAM... You should not be able to render anything in Iray with it on W10 and DS 4.20

Windows 10 steals 1GB of VRAM just because.
DS takes about 200MB's of VRAM
A GTX card uses about 1GB of VRAM to emulate the RTX functions on software
While rendering Iray, the process needs "Working Space in VRAM, which by default is 1.7GB's on DS 4.15 and 1.9GB's on DS 4.20 if there is enough space, if the amount of available "Working Space" gets below 1GB, one starts noticing the rendering times getting lower. The lowest amount of "Working Space" I have seen on a render that was still done on GPU was around 360MB's (very slow)

Attached is a test I made some time ago to see how much RAM and VRAM was used while rendering in IRAY

Case a) just one lightweight G8 figure with lightweight clothing and hair
Case b) four similar G8 characters with architecture
Case c and d) started increasing SubD on the characters to see at which point the rendering would drop to CPU

"RAM/GB" and "VRAM/MB" taken from GPU-Z, "DS Log/GiB" taken from DS Log, no other programs were running but DS and GPU-Z
The "DS Log/GiB" is the sum of Geometry usage, Texture usage and Working Space - After Geometry and Textures, there should still be at least a Gigabyte of VRAM available for the Working space => In my case, Geometry + Textures should not exceed 4.7GiB

Note; Case c) was already using 38GB's of RAM, even though the rendering was done on the GPU, Case d) when rendering on CPU the RAM usage went almost over my 64GB's

Tests made using RTX 2070 Super (8GB), i7-5820K, 64GB's of RAM on W7 Ultimate and DS 4.15 (Note; W10 uses 700MB's more VRAM and a GTX card takes an additional 1GB of VRAM)

StratDragon

check your driver versions. 

check your render settings in Iray under the Progressive section. Check you min/max and time to make sure they're not to short

I use GPU-Z but you can also open the task manager, go to performance tab, make sure you have your Nvidia GPU selected, you may see an integrated chip if your CPU has that. Change 3D in the dropdown to Cuda and render.