Modesetting+TearFree hurts Nvidia prime pacing #3680

Select the version

25.2.X

Describe your issue

Programs that run in the Nvidia dGPU (driver 580) and are rendered in iGPU (running Modesetting with TearFree enabled) via Prime Offload, have some kind of wrong pacing, and the first frames are always jumping, and also sometimes it keeps running at wrong FPS. When it keeps the wrong pacing, it almost always fixes when I move the window to another output or resize it, or just wait some time.
I did some research with Claude llm and we found that the times when the program runs wrong (llm called it "judder"), there is more than 1 frame presenting at the same time, or something like this, it's not very easy for me to understand. And it did not had a good solution.
Then finally I tried bisect, and discovered that reverting 2e31b2f stops the odd behavior.

There is #1588 but I don't think it's duplicate, because that is about crashing, and my system does not crash -- it crashed like that issue with Nvidia driver 535 that I used with Xorg 21, now the driver 580 is stable in XLibre too.

Steps to reproduce

Start X server with modesetting DDX and TearFree enabled + Nvidia proprietary only for Prime offload;
Try starting vkcube - it should use Nvidia;
If it started normally, close and start vkcube again.

What did you expect?

The animation should always run smoothly from the very start (as it always did with XLibre 25.1)

Additional Information

I recorded one of the worst times it happened, but in general it's less dramatic, but always hurts when gaming.
https://www.youtube.com/watch?v=_aI6epy4Ms4

Extra fields

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