Ubuntu20.04.3 setted Mosaic,screens have no signal

nvidia-bug-report.log.gz (1.2 MB)

Previous forum posts: Ubuntu20.04 setted BaseMosaic on,screens have no signal - Graphics / Linux / Linux - NVIDIA Developer Forums
Different from last year’s post, please help…
After posting last year, due to the urgency of other projects, we didn’t study this problem again.Now I finally have time, so I come to study this problem again. I also hope experts can give me advice.

Now I have a lenovo P920 workstation with 4 graphics cards, QUADRO RTX 4000.Every graphics card connected to a 4K monitor using dp interface.
My OS is ubuntu20.04.3 lts, when i installed my os,I executed the following command:
sudo apt update
sudo apt upgrade
sudo ubuntu-drivers auto install
sudo reboot
After system restart,i run the command sudo nvidia-settings. In primary screen,I enable BaseMosaic ,and enabled other monitor with “Configuration : x screen 0”,then i apply settings and saved it in xorg.conf.
Section “Device”
Identifier “Device0”
Driver “nvidia”
VendorName “NVIDIA Corporation”
BoardName “Quadro RTX 4000”
BusID “PCI:24:0:0”
EndSection

Section “Screen”
Identifier “Screen0”
Device “Device0”
Monitor “Monitor0”
DefaultDepth 24
Option “Stereo” “0”
Option “nvidiaXineramaInfoOrder” “DFP-2”
Option “metamodes” “GPU-3769bf8b-8596-42f1-4dd1-c937a9abd336.DP-2: nvidia-auto-select +0+0, GPU-89ee868c-a213-2a18-cd83-069d619e0603.DP-1-2: nvidia-auto-select +3840+0, GPU-49aa6c0e-7468-34a3-0816-813020bcb4a3.DP-2-2: nvidia-auto-select +7680+0, GPU-01cd901e-0b40-ee13-b697-49dc3377024b.DP-3-3: nvidia-auto-select +11520+0”
Option “MultiGPU” “Off”
Option “SLI” “Mosaic”
Option “BaseMosaic” “off”
SubSection “Display”
Depth 24
EndSubSection

Here:
Option “MultiGPU” “Off”
Option “SLI” “Mosaic”
Option “BaseMosaic” “off”
I read Chapter 30. Configuring SLI and Multi-GPU Mosaic,Document tips: Quadro Series graphics card, SLI mosaic for multi graphics card, multigpu for single graphics card, and basemosaic for geforce series.
So I set the xorg.conf as above.But it still doesn’t work,even I added the following configuration, which is also not worked:Option “AllowEmptyInitialConfiguration” “True” or Option “AllowEmptyInitialConfiguration”

Then i reboot again,After the restart, the displays (four monitors) all have no signal.But use other computer , i can connect the workstation with ssh.In /var/log/syslog ,i found this:

Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) NVIDIA GLX Module 470.86 Tue Oct 26 21:51:04 UTC 2021
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) NVIDIA: The X server supports PRIME Render Offload.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (WW) NVIDIA(GPU-0): The “BaseMosaic” X configuration option should be used for
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (WW) NVIDIA(GPU-0): this configuration instead of the “SLI” “Mosaic” option.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (WW) NVIDIA(GPU-0): The “BaseMosaic” option will be assumed. Please see
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (WW) NVIDIA(GPU-0): Chapter 30: Configuring SLI and Multi-GPU Mosaic and
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (WW) NVIDIA(GPU-0): Appendix B: X Config Options for more information.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) NVIDIA(GPU-0): NVIDIA SLI enabled.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) NVIDIA(GPU-0): Failed to select a display subsystem.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) NVIDIA(GPU-0): Only one GPU will be used for this X screen.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) NVIDIA(GPU-0): The NVIDIA graphics device PCI:24:0:0 is part of an active SLI
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) NVIDIA(GPU-0): configuration and is currently unavailable for single GPU
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) NVIDIA(GPU-0): rendering. Please see Chapter 30: Configuring SLI and
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) NVIDIA(GPU-0): Multi-GPU Mosaic in the README for troubleshooting
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) NVIDIA(GPU-0): information.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) *** Aborting ***
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) NVIDIA(0): Failing initialization of X screen
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) UnloadModule: “nvidia”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) UnloadSubModule: “glxserver_nvidia”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) Unloading glxserver_nvidia
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) UnloadSubModule: “wfb”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) UnloadSubModule: “fb”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: () NVIDIA(G0): Depth 24, (–) framebuffer bpp 32
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (==) NVIDIA(G0): RGB weight 888
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (==) NVIDIA(G0): Default visual is TrueColor
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (==) NVIDIA(G0): Using gamma correction (1.0, 1.0, 1.0)
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) Applying OutputClass “nvidia” options to /dev/dri/card1
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (
) NVIDIA(G0): Option “Stereo” “0”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: () NVIDIA(G0): Option “nvidiaXineramaInfoOrder” “DFP-2”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (
) NVIDIA(G0): Option “SLI” “Mosaic”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: () NVIDIA(G0): Option “MultiGPU” “Off”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (
) NVIDIA(G0): Option “BaseMosaic” “off”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: () NVIDIA(G0): Option “AllowEmptyInitialConfiguration”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (
) NVIDIA(G0): Stereo disabled by request
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: () NVIDIA(G0): NVIDIA SLI Mosaic mode selected.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (
) NVIDIA(G0): NVIDIA Multi-GPU disabled.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (WW) NVIDIA(G0): SLI is available only on screen 0. Disabling SLI.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) NVIDIA(G0): Only one X screen is supported when SLI is enabled. Disabling
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) NVIDIA(G0): this screen.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) NVIDIA(G0): Failing initialization of X screen
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) NVIDIA(G1): (GPU-2) already has an X screen assigned; skipping this GPU
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) NVIDIA(G1): screen
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) NVIDIA(G1): Failing initialization of X screen
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) NVIDIA(G2): (GPU-3) already has an X screen assigned; skipping this GPU
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) NVIDIA(G2): screen
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) NVIDIA(G2): Failing initialization of X screen
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) UnloadModule: “nvidia”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) UnloadSubModule: “wfb”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) UnloadSubModule: “fb”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) UnloadModule: “nvidia”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) UnloadSubModule: “wfb”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) UnloadSubModule: “fb”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) UnloadModule: “nvidia”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) UnloadSubModule: “wfb”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (II) UnloadSubModule: “fb”
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) Screen(s) found, but none have a usable configuration.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE)
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: Fatal server error:
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) no screens found(EE)
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE)
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: Please consult the The X.Org Foundation support
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: #011 at http://wiki.x.org
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: for help.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) Please also check the log file at “/var/lib/gdm3/.local/share/xorg/Xorg.0.log” for additional information.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE)
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1787]: (EE) Server terminated with error (1). Closing log file.
Jan 26 15:23:55 hengda-ThinkStation-P920 /usr/lib/gdm3/gdm-x-session[1783]: Unable to run X server
Jan 26 15:23:55 hengda-ThinkStation-P920 gdm3: Child process -1783 was already dead.
Jan 26 15:23:55 hengda-ThinkStation-P920 systemd[1]: session-c1.scope: Succeeded.
Jan 26 15:23:55 hengda-ThinkStation-P920 goa-daemon[1825]: goa-daemon version 3.36.1 starting


Jan 26 15:24:12 hengda-ThinkStation-P920 kernel: [ 33.060551] nvidia-modeset: ERROR: GPU:0: Failed to query display engine channel state: 0x0000c57d:0:0:0x00000057
Jan 26 15:24:12 hengda-ThinkStation-P920 kernel: [ 33.060605] nvidia-modeset: ERROR: GPU:0: Failed to query display engine channel state: 0x0000c57e:1:0:0x00000057
Jan 26 15:24:12 hengda-ThinkStation-P920 kernel: [ 33.060651] nvidia-modeset: ERROR: GPU:0: Failed to query display engine channel state: 0x0000c57e:0:0:0x00000057
Jan 26 15:24:12 hengda-ThinkStation-P920 kernel: [ 33.060694] nvidia-modeset: ERROR: GPU:0: Failed to query display engine channel state: 0x0000c57e:3:0:0x00000057
Jan 26 15:24:12 hengda-ThinkStation-P920 kernel: [ 33.060737] nvidia-modeset: ERROR: GPU:0: Failed to query display engine channel state: 0x0000c57e:5:0:0x00000057
Jan 26 15:24:12 hengda-ThinkStation-P920 kernel: [ 33.060779] nvidia-modeset: ERROR: GPU:0: Failed to query display engine channel state: 0x0000c57e:7:0:0x00000057

=========================================
According to the log file,it says i should use basemosaic,but if i set option basemosaic on,it is also no signal output to four monitors , as My post last year.

Use ssh i sudo vi /etc/X11/xorg.conf , changed Option “BaseMosaic” “on” to Option “BaseMosaic” “off”, Option “SLI” “Off” and reboot,then all four monitors have signal,

It’s puzzling if I install Ubuntu 20.04. Do the above mosaic settings, and there is no signal on the four monitors, but if I install Ubuntu 18. 04. Set the mosaic as above,it works! Then I upgrade OS to Ubuntu to 20.04 using the command:do-release-upgrade. Last year, I can bypass this problem and use it normally,means the four monitors all have single and work right . Why? Before and after the upgrade, xorg.conf has not changed.

This problem has bothered me for a long time. Is there a solution? I also read Chapter 30, so I used the option “SLI” “Mosaic”, but it really didn’t work.

=========
hengda@hengda-ThinkStation-P920:/etc/X11$ lspci | grep VGA
18:00.0 VGA compatible controller: NVIDIA Corporation TU104GL [Quadro RTX 4000] (rev a1)
3b:00.0 VGA compatible controller: NVIDIA Corporation TU104GL [Quadro RTX 4000] (rev a1)
86:00.0 VGA compatible controller: NVIDIA Corporation TU104GL [Quadro RTX 4000] (rev a1)
af:00.0 VGA compatible controller: NVIDIA Corporation TU104GL [Quadro RTX 4000] (rev a1)

hengda@hengda-ThinkStation-P920:/etc/X11$ lspci -t
-±[0000:d7]-±05.0
| ±05.2
| ±05.4
| ±0e.0
| ±0e.1
| ±0f.0
| ±0f.1
| ±12.0
| ±12.1
| ±12.2
| ±12.4
| ±12.5
| ±15.0
| ±16.0
| ±16.4
| -17.0
±[0000:ae]-±00.0-[af]–±00.0
| | ±00.1
| | ±00.2
| | -00.3
| ±05.0
| ±05.2
| ±05.4
| ±08.0
| ±09.0
| ±0a.0
| ±0a.1
| ±0a.2
| ±0a.3
| ±0a.4
| ±0a.5
| ±0a.6
| ±0a.7
| ±0b.0
| ±0b.1
| ±0b.2
| ±0b.3
| ±0c.0
| ±0c.1
| ±0c.2
| ±0c.3
| ±0c.4
| ±0c.5
| ±0c.6
| ±0c.7
| ±0d.0
| ±0d.1
| ±0d.2
| -0d.3
±[0000:85]-±00.0-[86]–±00.0
| | ±00.1
| | ±00.2
| | -00.3
| ±05.0
| ±05.2
| ±05.4
| ±08.0
| ±08.1
| ±08.2
| ±08.3
| ±08.4
| ±08.5
| ±08.6
| ±08.7
| ±09.0
| ±09.1
| ±09.2
| ±09.3
| ±09.4
| ±09.5
| ±09.6
| ±09.7
| ±0a.0
| ±0a.1
| ±0a.2
| ±0a.3
| ±0a.4
| ±0a.5
| ±0a.6
| ±0a.7
| ±0b.0
| ±0b.1
| ±0b.2
| ±0b.3
| ±0e.0
| ±0e.1
| ±0e.2
| ±0e.3
| ±0e.4
| ±0e.5
| ±0e.6
| ±0e.7
| ±0f.0
| ±0f.1
| ±0f.2
| ±0f.3
| ±0f.4
| ±0f.5
| ±0f.6
| ±0f.7
| ±10.0
| ±10.1
| ±10.2
| ±10.3
| ±10.4
| ±10.5
| ±10.6
| ±10.7
| ±11.0
| ±11.1
| ±11.2
| ±11.3
| ±1d.0
| ±1d.1
| ±1d.2
| ±1d.3
| ±1e.0
| ±1e.1
| ±1e.2
| ±1e.3
| ±1e.4
| ±1e.5
| -1e.6
±[0000:80]-±04.0
| ±04.1
| ±04.2
| ±04.3
| ±04.4
| ±04.5
| ±04.6
| ±04.7
| ±05.0
| ±05.2
| ±05.4
| ±08.0
| ±08.1
| -08.2
±[0000:5d]-±05.0
| ±05.2
| ±05.4
| ±0e.0
| ±0e.1
| ±0f.0
| ±0f.1
| ±12.0
| ±12.1
| ±12.2
| ±12.4
| ±12.5
| ±15.0
| ±16.0
| ±16.4
| -17.0
±[0000:3a]-±00.0-[3b]–±00.0
| | ±00.1
| | ±00.2
| | -00.3
| ±05.0
| ±05.2
| ±05.4
| ±08.0
| ±09.0
| ±0a.0
| ±0a.1
| ±0a.2
| ±0a.3
| ±0a.4
| ±0a.5
| ±0a.6
| ±0a.7
| ±0b.0
| ±0b.1
| ±0b.2
| ±0b.3
| ±0c.0
| ±0c.1
| ±0c.2
| ±0c.3
| ±0c.4
| ±0c.5
| ±0c.6
| ±0c.7
| ±0d.0
| ±0d.1
| ±0d.2
| -0d.3
±[0000:17]-±00.0-[18]–±00.0
| | ±00.1
| | ±00.2
| | -00.3
| ±05.0
| ±05.2
| ±05.4
| ±08.0
| ±08.1
| ±08.2
| ±08.3
| ±08.4
| ±08.5
| ±08.6
| ±08.7
| ±09.0
| ±09.1
| ±09.2
| ±09.3
| ±09.4
| ±09.5
| ±09.6
| ±09.7
| ±0a.0
| ±0a.1
| ±0a.2
| ±0a.3
| ±0a.4
| ±0a.5
| ±0a.6
| ±0a.7
| ±0b.0
| ±0b.1
| ±0b.2
| ±0b.3
| ±0e.0
| ±0e.1
| ±0e.2
| ±0e.3
| ±0e.4
| ±0e.5
| ±0e.6
| ±0e.7
| ±0f.0
| ±0f.1
| ±0f.2
| ±0f.3
| ±0f.4
| ±0f.5
| ±0f.6
| ±0f.7
| ±10.0
| ±10.1
| ±10.2
| ±10.3
| ±10.4
| ±10.5
| ±10.6
| ±10.7
| ±11.0
| ±11.1
| ±11.2
| ±11.3
| ±1d.0
| ±1d.1
| ±1d.2
| ±1d.3
| ±1e.0
| ±1e.1
| ±1e.2
| ±1e.3
| ±1e.4
| ±1e.5
| -1e.6
-[0000:00]-±00.0
±04.0
±04.1
±04.2
±04.3
±04.4
±04.5
±04.6
±04.7
±05.0
±05.2
±05.4
±08.0
±08.1
±08.2
±11.0
±11.1
±11.5
±14.0
±14.2
±16.0
±16.2
±16.3
±17.0
±1d.0-[01]–
±1d.2-[02]----00.0
±1f.0
±1f.2
±1f.3
±1f.4
±1f.5
-1f.6

nvidia-bug-report.log.gz (1.2 MB)

Please run

grep nvidia /etc/modprobe.d/* /lib/modprobe.d/*

to find a file containing

options nvidia-drm modeset=1

and change 1 to 0
then run

sudo update-initramfs -u

and reboot.
Then try again using an xorg.conf like
https://forums.developer.nvidia.com/t/ubuntu20-04-setted-basemosaic-on-screens-have-no-signal/177765/5?u=generix

This method is indeed feasible and has solved the problem! Thank you very much for @ generix’s technical guidance!!

Learn from experts!

Here are a few more questions please:

  1. Why does the options NVIDIA DRM modeset = 1 change this parameter to take effect? What does this parameter do?

  2. I see the system I upgraded from 18.04 through the do-release-upgrade command. This parameter is indeed 1, not 0. Why does the upgraded system not have this problem? What could be the reason?

  3. According to the configuration of my workstation, that is, one workstation is equipped with four Quadro RTX 4000 graphics cards, which are combined into a large desktop. My xorg.conf content ,Should I use basemosaic or SLI mosaic ? If I equipped only one graphics card (rtx4000) that uses four interfaces to form a large desktop with four screens, should I use the basemosaic or multigpu option?
    4.According to the previous reading in Chapter 30, the cooperation of multiple graphics cards should use SLI, single graphics card should use multigpu, and non Quadro Series graphics card should use basemosaic. Is there a mistake in my understanding…I must admit that I really don’t fully understand this

Thanks again for generix’s guidance, which has really solved the problem I’ve been perplexing for a year. Bow!

  1. About the nvidia-drm modeset=1and known issue with sli/mosaic please see this:
    https://download.nvidia.com/XFree86/Linux-x86_64/460.67/README/kms.html
  2. The option is set by some Ubuntu packages, also depending on driver version. Somteimes it’s set, sometime unset.
  3. If you only have one RTX with four monitor connected, you don’t need any Mosaic setting, this is only for multiple gpus. It’s ignored in that case.
  4. All those settings once had a distinctive use-case, AFAIK multigpu for dual-gpu boards like the NVS810, SLI=Mosaic for Quadro-systems with SLI/NVlink bridges/Quadro-Sync, BaseMosaic for Quadro/Geforce without bridges.
    With current drivers, I don’t think there’s a difference anymore, from my observations the driver auto-configures it, regardless of setting.
    If you have NVLink-bridges installed, you might test if setting sli mosaic instead of basemosaic changes anything regarding video memory usage.