hardware.nvidia.forceFullCompositionPipeline disables second monitor

[gepbird]

Describe the bug

By enabling hardware.nvidia.forceFullCompositionPipeline, it fixes the screen tearing as expected, but disables a 2nd monitor.

Steps To Reproduce

Steps to reproduce the behavior:

1. Copy the default nvidia settings from the wiki
2. Change open to false and forceFullCompositionPipeline to true
3. Rebuild and reboot
4. Observe that only one screen is turned on and detected by nvidia

Expected behavior

Second monitor works as before.

Screenshots

Additional context

Both monitors work when hardware.nvidia.forceFullCompositionPipeline = false.

Notify maintainers

@schuelermine

Metadata

[user@system:~]$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 6.1.55, NixOS, 23.11 (Tapir), 23.11.20231006.87828a0`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.17.0`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

[gepbird]

Nevermind, I can enable second monitor in nvidia settings. Still weird that forceFullCompositionPipeline disables it.

[gepbird]

Changing settings in the GUI doesn't preserve between reboots. Is there a nix option for controlling nvidia-settings?

[gepbird]

When exporting the xserver configuration from nvidia settings, both monitors are in screen section metamodes:

    Option         "metamodes" "HDMI-0: nvidia-auto-select +1920+0, DVI-D-0: nvidia-auto-select +0+0"

but with hardware.nvidia.forceFullCompositionPipeline = true, no monitors are specified, so I assume only the first monitor it founds will work:

  Option         "metamodes" "nvidia-auto-select +0+0 {ForceFullCompositionPipeline=On}"

[antoningfors]

My current workaround is to configure FullCompositionPipeline using the services.xserver.screenSection option. For my two monitor setup I configure ForceFullCompositionPipeline individually on each monitor.

services.xserver.screenSection = ''Option "metamodes" "nvidia-auto-select {ForceFullCompositionPipeline=On}, nvidia-auto-select {ForceFullCompositionPipeline=On}"'';