Cycles Various Render Times
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Authored By

	David Cherrie (davidcherrie)
	Nov 4 2022, 1:21 PM

Description

System Information
Operating system: Windows 11
Graphics card: RTX 3080

Blender Version
Broken: All versions
Worked: Never

Short description of error
When rendering in Cycles with large scenes, I get hugely variations in performance randomly. Currently I'm working in a very large scene which can render in about 4 minutes. But many times when starting the render, with different attempts I will get render times that vary from 10 minutes but mainly 50 to 70 minutes. To fix the issues, I literally cancel the render and just keep pressing the render button until I see the sample count progressing at a reasonable rate. Or if I get that frustrated, I will close the program and open then press hit render.

Exact steps for others to reproduce the error
Can reliably reproduce across any of my large projects over the years. It always happens when I'm rendering at 4K resolution even though I use tiling to render it.

Event Timeline

David Cherrie (davidcherrie) created this task.Nov 4 2022, 1:21 PM

Are you sure that this has always been an issue? Can you test with Blender 2.93 (pre Cycles X) and a 3.3 or 3.4 Beta build?

Also what tiling settings do you use? Is the issue also happening with the default of 2048?

If you run Blender as administrator, does it still happen?

@Thomas Dinges (dingto) Just tested and the issue is the same in 2.93 as well as 3.3.1

Trying without tilling, the render time is estimated as 80 minutes but after leaving it for several minutes, it goes down to 40.
Using tiling set to 2048, around the same time as before. 65-70 minutyes and then after several minutes, it estimates around 40 minutes.
Using tiling set to 540, starts off at 45 minutes and is pretty constant with the amount of time remaining.
Using tiling set to 128 render times vary from 10 to 30 minutes.

I'm aware the Cycles X shouldn't need tiling but its the only way I can render faster reliably. I've seen Blender when using no-tiling on this project go from 1 sample to 3 in 4 seconds, but most of the time it takes 60+ seconds to go from 1 sample to 3.

@Charles (mtoronto) Is the same no matter if you are in Administrator or not.

Charles (mtoronto) removed a subscriber: Charles (mtoronto).Nov 12 2022, 4:16 AM

So have just installed my RTX 4090 and used the same scene which has varied from hours to complete or just 8 or so minutes. With the 4090, I rendered the scene multiple times which took less than 3 minutes. Now all of a sudden without changing anything, it has slowed down to a speed predicting it will take 3 hours to complete. With the 4090 with tiling set to 128, it would complete 3-4 tiles per second. Now it is taking 10+ seconds to do each tile.

What is going on?

@David Cherrie (davidcherrie) Thank you for testing.

It's difficult to say more without a test scene in which the issue happens for you. I am not aware of any other bug report that reports these time differences. Do you have any other programs running that access the GPU and could cause the slowdown?

Thomas Dinges (dingto) added a project: Render & Cycles.Nov 18 2022, 3:49 PM

No activity for more than a week. As per the tracker policy we assume the issue is gone and can be closed.

Thanks again for the report. If the problem persists please open a new report with the required information.

No, all other programs and tasks are closed, and will always happen after a fresh restart of the computer.

Cycles Various Render TimesClosed, ArchivedPublicActions

Description

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Cycles Various Render Times
Closed, ArchivedPublic
Actions