Iray Reports Incorrect VRAM Usage

joeshelton0001_f3a8ae879b

Hey guys --

So after a whooole lot of debugging I've discovered Iray is reporting incorrect memory usage for geometry.  There are a ton of threads where people have reported Iray stops using GPUs and reverts to CPU even when it's using nowhere near the full VRAM of their GPU.  This seems to happen quite a lot when people use displacement since higher displacement subdivision levels are necessary for Daz assets that were created with 3Delight in mind to look good.

Well, it turns out that Iray is using all the VRAM, but it's just not reporting it.

The way to trigger this is to take an object and see how much VRAM Iray allocates to geometry at base resolution.  Multiply by four for each level of subdivision.  You can see Iray do this for the first couple levels of subdivision.  Once the object begins to pass somewhere around the 150 MB mark it will stop reporting higher levels of subdivision.  

Example: An object requires 10 MB at base resolution.  At subdivision level 1 it will require 40 MB.  At 2, it will require 160 MB.  At 3, Iray will report it at 160 MB, even though it really requires 640 MB.

I'm convinced this is a source of a lot of confusion with regard to Iray reverting to CPU, and it's bound to happen even more as long as Daz produces HD morphs that require subdivision level 4 for characters.  Hopefully someone can do something with this information.

Padone

Yes. Unfortunately the log gives bad values. This has also been reported as a bug report. To me they replied they are not able to reproduce the issue. That seems quite unlikely to me. To others they replied it's a nvidia bug so they can do nothing. Short story the DAZ team doesn't seem to be able to find a solution.

The only way to get a real measure is to use gpu-z or similar tools. Do not trust the log.

 

p.s. And in my opinion if they can't fix it then it should be reported in the known issues that the log is not to be trusted.