Tearing / sluggish desktop since recent 18.04 update with AMD hardware

[Mike]

I did a full update of my system which has been running 18.04 since the beta 2 update and I've noticed now that the desktop feels quite sluggish. The last update I did was about 5 days ago. I'm not sure which package was the culprit as several were updated (30+).

However - I think it has something to do with Gnome. I have a 75 Hz monitor, and it seems like Gnome animations, as well as just actions like moving windows around, feel like they're rendering at a lower frame rate. There is a lot of jitter too almost like tearing.

Moving the mouse cursor around feels like 75 Hz though (super smooth), as well as when I play games. Had no issues prior to running 'apt upgrade'. And I can confirm my monitor is running @ 75 Hz.

I'm running the stock Ubuntu kernel currently but I did try installing the most recent stable kernel (4.16.2) and that exhibited the same issue. One thing I did notice, is that setting the flag amdgpu.dc=0 in my Grub config did fix the tearing and general lag issues with moving windows around. However, it isn't a complex fix as that instead introduced stuttering with the mouse cursor.

With a fresh Beta 2 installed (no package updates) this tearing/lag issue is not present. It is also not present when using 16.04 with an updated kernel. Additionally using Wayland instead of X.org I don't notice these issues but that has the limitation effect of not being able to run at higher refresh rates in my testing.

System specs:

Threadripper 1950X
64 GB RAM
Radeon Pro WX7100
LG 38UC99 monitor (3840x1600 res).

Description: Ubuntu Bionic Beaver (development branch)
Release: 18.04

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. It seems that your bug report is not filed about a specific source package though, rather it is just filed against Ubuntu in general. It is important that bug reports be filed about source packages so that people interested in the package can find the bugs about it. You can find some hints about determining what package your bug might be about at https://wiki.ubuntu.com/Bugs/FindRightPackage. You might also ask for help in the #ubuntu-bugs irc channel on Freenode.

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[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.