nvidia-xrun hangs with modeset=1 kernel option and nvidia-xrun-pm service enabled

[gtarsia]

I noticed in another issue @michelesr asked someone to try modeset=0 (but as a default in /etc/default/nvidia-xrun, while I'm setting it as a kernel option).

The problem is that if I set modeset=0 (as kernel opt, haven't tried as default) I get crazy screen tearing.

But if I set modeset=1, the nvidia-xrun-pm service makes nvidia-xrun not run at all (it works otherwise with the service disabled).

1. Can the tearing be fixed even with modeset=0?
2. Does it make a difference whether I set it as a kernel opt or as a default?

Thank you devs for working on this project.

[michelesr]

@zzyyxxww tearing is caused by lack of sync between the two graphic cards (see this). PRIME sync can't be enabled when modeset is disabled, so I don't think is possible to fix the tearing without modeset. Setting it as a kernel option is totally different from setting it in the nvidia module options... and because the module is loaded by nvidia-xrun, the modeset option must be set in the nvidia-xrun config.

[sudopluto]

what i've noticed is that in Fedora w/ rpmfusion, "nvidia_drm modeset = 1" seems to be added to grub. removing that allowed nvida-xrun to run, and once nvida-xrun was running, the nvidia session had modeset enabled & there was no screen tearing.

notes here: https://www.reddit.com/r/Fedora/comments/ca0ca7/notes_on_how_to_use_nvidiaxrun_with_fedora_30/