Prime: weird tearing

I’m using the integrated gpu to display frames rendered by the nvidia gpu.
Prime synchronization works, and i’m able to dynamically switch it on/off.
There’s a problem tough, when i switch prime synchronization off to reduce the visible lag, the tearing it produces, is much, much worse than the one i observe when i use the nvidia gpu directly.

To explain it better, i tried to play a 60fps video without vsync, the display is set to 60hz, no compositor is running, tearing is expected.

mpv 60fps.mkv --opengl-swapinterval=0

Since display refresh rate and video fps matches, one would expect to see a single line more or less at the same fixed position on the screen over time, and indeed running it on the nvidia gpu attached directly on the monitor produces that.
But if i do the same on the prime configuration (with prime synchronization turned off), i see “tearing lines” quickly crossing the screen from bottom to up, and slightly changing the fps of the video seems to make no difference.

Without vsync, the prime experience is much worse than without prime.

nvidia-bug-report.log.gz (245 KB)