Why is Iray not using my GPU?
Morokei
Posts: 0
According to Task Manager, Daz Studio only uses my CPU while rendering. Zero GPU usage. I let a render run for over an hour and this never changed. Sometimes CPU usage got up to 100%, but GPU never went above 0%.
In the Render Settings > Advanced > Hardware, I have:
- GPU checked and CPU unchecked (in both Photoreal and Interactive(Biased))
- In Scheduling
- CPU Load Limit: 6
- CPU Thread Affinity: unchecked
- Allow CPU Fallback unchecked
- Allow GPU Detection checked
- Check GPU Driver Version checked
Aren't these settings supposed to keep it all on the GPU?
Are my settings wrong? Is that CPU Load Limit Is Task Manager wrong? I'm so confused.
- DS Version 4.20.0.2
- Windows 10
- NVIDIA GeForce GTX 1660 Ti
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Comments
The last time I had this issue, I had a GPU with a VRAM amount not enough to handle the scene.
Is your scene too heavy for your GPU?
What do you have there? How many G8 or G9 characters?
Task Manager is not a good tool for checking, unless one knows how to set it up and how to read the results.
GPU-Z is a lot better.
In task Manager check the performance tab, select the GPU, and set one of the graphs to CUDA (if there - if not try Compute 0).
Your GPU is definitely doing the render, despite what Windows tells you (see above for how to get a clearer picture). As you've unchecked 'fallback to CPU' your renders would just be an almost instant black screen if you exceeded the available VRAM on your card. If you want to be sure, the Windows report of the GPU's temperature is pretty accurate - it won't be idling. The fact that you haven't exceeded your card's VRAM surprises me a little bit as 6GB really isn't enough these days. RTX emulation (for non-RTX cards, obviously!) takes up about 2GB, although I believe you can still disable this memory useage by setting 'Ray Tracing Low Memory' to On in Render Settings -> Optimization at the cost of speed but I haven't ever used this or checked it. Windows will easily hack off another 0.5GB, iRay will also reserve some workspace depending on the resolution of your render which doesn't leave you very much for your scenes.
Windows 10/11 has some components which will happily run your CPU at 100% unless they get an interrupt. The easiest way to do this is to start Task Manager and then minimise it. It's a quick and dirty hack but it works, the alternative being messing about with the .NET framework which I'd hesitate to recommend.
If you can, have a think about adding an RTX card to your PC - an addition of something like an RTX 3060 as a standalone card whilst you used your 1660Ti to drive the monitors would make a massive difference to your setup. 32GB of system RAM to run this comfortably. There are better cards than the 3060 some of which I think, even though they're more expensive, are actually better value but it's currently the cheapest way to drag your PC to a spec. which is comfortable for rendering.
Similar issue for me on a new videocard bought specifically to speed renders. The log file explicitly says:
2026-05-21 06:05:04.635 Iray [INFO] - IRAY:RENDER :: 1.0 IRAY rend info : Initializing local rendering.
2026-05-21 06:05:04.644 Iray [INFO] - IRAY:RENDER :: 1.0 IRAY rend info : CPU: using 32 cores for rendering
2026-05-21 06:05:04.644 Iray [INFO] - IRAY:RENDER :: 1.0 IRAY rend info : Rendering with 1 device(s):
2026-05-21 06:05:04.644 Iray [INFO] - IRAY:RENDER :: 1.0 IRAY rend info : CPU
2026-05-21 06:05:04.644 Iray [INFO] - IRAY:RENDER :: 1.0 IRAY rend info : Rendering...
2026-05-21 06:05:04.644 Iray [INFO] - IRAY:RENDER :: 1.21 IRAY rend progr: CPU: Processing scene...
Any clues on why it's not using the GPU. I'm running on a 1-version-ago studio as I've been a 3 Delight user and until iray works for me, I'm not losing that capability. 4.24.0.3
FWIW, a similar render on my "old" non Nvidia card took 7 minutes and this test took 11 minutes. Going backwards!
If I untick CPU in the hardware tab, the render fails "rend error: Cannot render: found no usable devices. Please update your NVIDIA driver (www.nvidia.com) to at least 537.13, or enable CPU rendering.
That driver call (537.13) appears to have no relation to the card's driver 32.0.15.9636.
What GPU did you buy? If it's a 50xx card, they don't work for Iray rendering in DS4, they only work in DS2026.
Ahhhh. Bugger! It is indeed a 50xx. Pfffft goes $1300. At least for the moment. Cheers.
Before I get even halfway enthusiastic about iray - I whacked in an older vid-card I had - 1060 6GB and ran my comparison render. 24 minutes. That's twice as long as CPU rendering and 48 times as long as the same scene in 3Delight. This card has 1280 CUDO cores and 6GB of VRAM, which was fully occupied during the render. But if I extrapolate to my new 50xx card with 8000-something CUDO cores, 24 minutes might become 4 minutes which is 8 times as long as 3Delight. Given all the enthusiasm for iray, what am I not understanding?
First, Daz no longer supports 3DLight. So if you have 4.24, 3DLight renders are only fast becase they don't happen.
Second, the Daz2026 Beta works fairly well as long as you don't need access to plugins. Most workflows for folks with 50xx GPUs is set the scene with 4.24 and then render in Daz6. So, no $1300 down the drain.
Third, have you compared the look of a 3DLight render to one made with IRAY? There are not "the same" and thus the timing comparison is apples to oranges.
Are you sure the 1060 was even used for rendering? Iray GPU render taking longer than with CPU is not usual. Beside 6GB VRAM is not much, and for non-RTX cards a part of that VRAM is used to emulate the RTX features, so it's quite possible the render dropped to CPU at some point.
Extrapolating render times from the number of cores between GPU generations will not give you any meaningful results, as core performance is much higher in newer cards.
People like using Iray because it's a physically-based render engine, and it's easy to get photorealistic renders out of it. That has nothing to do with speed relatively to 3DL (though when rendering with a recent GPU the render speed is usually quite good).
CPU fallback was off, so I'm assuming it was all GPU - but that's just an assumption. What do you think of as "usually quite good" render times? And if GPU render takes longer than CPU, why bother with GPU?? I have a fairly mighty CPU, because that was needed for brisk 3Delight renders.
GPU render is supposed to be much faster than CPU. As in, tens of times faster. Which is why I'm surprised when you say your test was slower than CPU.