Multiple displays on POP OS

[aryehw]

Distribution (run cat /etc/os-release):

NAME="Pop!_OS"
VERSION="20.04 LTS"
ID=pop
ID_LIKE="ubuntu debian"
PRETTY_NAME="Pop!_OS 20.04 LTS"
VERSION_ID="20.04"
HOME_URL="https://pop.system76.com"
SUPPORT_URL="https://support.system76.com"

Related Application and/or Package Version (run apt policy $PACKAGE NAME):
gnome-shell:
Installed: 3.36.4-1ubuntu120.04.2pop1159787444820.04260a1a7
Candidate: 3.36.4-1ubuntu120.04.2pop1159787444820.04260a1a7
Version table:
*** 3.36.4-1ubuntu120.04.2pop1159787444820.04260a1a7 1001
1001 http://ppa.launchpad.net/system76/pop/ubuntu focal/main amd64 Packages
100 /var/lib/dpkg/status
3.36.4-1ubuntu1~20.04.2 500
500 http://us.archive.ubuntu.com/ubuntu focal-security/main amd64 Packages
500 http://us.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
3.36.1-5ubuntu1 500
500 http://us.archive.ubuntu.com/ubuntu focal/main amd64 Packages

Issue/Bug Description:
Laptop display is 4K, run at 100% scaling. Second display is 1900x1080 (HD) , also run at 100%. In the past (until about 2 weeks ago), enable to render LoDPI displays at HiDPI resolution allowed me to move windows from one display to the next while retained correct window size relative to the display area.
Now that does not happen - moving a window form the 4K display to the HD display results in 4x magnification, which makes it impossible to use the second display without manually resizing the windows.
After reboot, the displays come up at 200% scaling, and the scaling does work, but then I have to use 2005 scaling, which means I do not get the benefit of my 4K display.

Steps to reproduce (if you know):
Connect an external HD monitor to a laptop with a 4K display run at 100% scaling,

Expected behavior:
The system should render the LoDPI display such that when dragging a windows from the HiDPI to LoDPI display it retains its relative size on the LoDPI display

Other Notes:
Used to work, but I cannot say exactly when it broke, other that within the last few weeks.
I am not sure how to move this to the proper forum - if the moderator can do that, I would appreciate it.

[bflanagin]

@aryehw two more question before we try to replicate the issue. What kind of GPU are you using (AMD,NVIDIA,INTEL)? And are you using the proprietary drivers?

[aryehw]

Thank you for your reply. Laptop is a Lenovo X1 Extreme (I think gen 1) with NVidia graphics using nvidia-driver-460 (I think 460.39, shown in pop shop under the installed tab).

[bflanagin]

If I'm reading your issue correctly I think the issue is with the new NVIDIA driver and how they changed the scaling options from the previous version.
For reference here is the document we have on the subject. I'll validate the document or make changes while you and I work out the issue.

[bflanagin]

@aryehw check to see if you are in Hybrid or Nvidia mode as it might have something to do with the issue, and check out a few of the other issues here in the hidpi-daemon. It seems a few of the symptoms you're experiencing are exhibited in them as well.

Picture for reference:

[aryehw]

Thank you for your replies. I am in NVidia mode. I once tried to use hybrid graphics, and that did not work. I cannot use the computer integrated graphics since that does not support two displays.

I will try to be more specific on what I mean when I say hybrid graphics did not work. Ever since moving to 20.04, I have often had trouble with the window manager getting stuck in various ways. For example, Firefox will stop responding, to all of my windows will not react to the mouse, or the computer will freeze for seconds every time I try to do something in a file-manager window. When that happens, often, the way out was
killall -3 gnome-shell
and that got things sane again. Before I found that workaround, I was rebooting 2-3 times/day - very aggravating.
Recently, this has been happening less often - I assume some of the upgrades helped. In any case, last time I tried hybrid graphics, these things made the system unusable, and I have not tried it since.