Iso values between 200 and 380 increase VRAM use making render impossible

BlueFingers

I am working on a dark scene with some dimmed lights, and in order to make a good render I started to use different ISO values.

I can render up to ISO 200 with no issues, I can render with ISO 380 or higher with no issues. But with ISO value in between 200 and 380, I run out of VRAM, which is I think strange. I am working with only 4GB of VRAM, but it still makes no sense to me.

Does anyone now what this is about?

ebergerly

I think there's something else going on, and any relationship between ISO setting and VRAM usage is, as they say, coincidental rather than causal. I just tried rendering a scene with ISO = 20, 200 & 300, and the GPU VRAM used by D|S was absolutely identical in all three cases. 

How are you measuring VRAM usage by D|S? Often I see people using incorrect measurement techniques. I suggest you use Task Manager, since W10 is responsible for assigning all computer hardware resources to the software apps that request those resources, including GPU VRAM (W10 uses its functions called "VidMm" and "VidSch" to allocate GPU VRAM). Keep in mind that many apps also use your GPU VRAM, so make sure you're measuring ONLY D|S. 

In Task Manager, under the Details tab, you'll see columns labelled "Name, PID", etc. Right click on one of the column headers, select "Select Columns" and choose any that include "GPU" in the title. This will give you a column showing Dedicated GPU Memory assigned to D|S by W10. 

BlueFingers

Could be something else, I really have no idea. I only ran DS, made sure minimal background services were running. I did not measure the VRAM use, but looked at the DS log after every try with a new ISO value.

I settled for 200 ISO which seems to be not far of the sweet spot for the scene, and am rendering it right now so I will be back with measurements later (I use GPU-Z, any benefits of using Task manager over GPU-Z?).

You wouldn't by any chance have a tip how to force Windows Desktop Window Manager to use the embedded Intel graphics chip would you? Could help to squeeze a bit more performance out of the VRAM and GPU.

ebergerly

IMO, GPU-Z and D|S log are pretty much a waste for the reasons I mentioned. Windows' job is to allocate GPU VRAM, not Iray or GPU-Z. And only Task Manager tells you BY PROCESS. And GPU-Z gets its info from W10.