Kubuntu 26.04 briefly freezing every so often

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1

Hello, I have an unusual and irritating issue with my brand new high-end desktop PC build on Kubuntu 26.04 LTS with Plasma Wayland (new minimal installation). It happens quite frequently that my screen freezes briefly, but then starts responding again. This usually happens 3 to 5 times in a row with like 1-second delays in-between while the freezes also last about 1 second each. After the freezing “spree” is done, the desktop becomes fully responsive again until the next batch of freezes happen. They seem to be triggered by things like rapid cursor movement or window dragging and usually happen about 10 to 20 seconds after some graphics-intensive activity has stopped. Funny thing is I also have CachyOS installed on another SSD where this doesn’t happen at all, so it likely not a hardware issue. Both systems use KDE Plasma on wayland. I use a 1440p (2560x1440) OLED monitor with up to 360Hz refresh rate.

Here are my observations so far:

  • The freezes seem to come in groups. They happen 3 to 5 times consecutively with about one second delay in-between.
  • They often happen a dozen seconds after some GPU-intensive activity has ceased e.g. heavy cursor wiggling, wobbly window dragging, glxgears.
  • They don’t happen while some gpu-intensive program is running (e.g. glxgears at 300Hz).
  • They happen on Kubuntu 26.04 LTS, but not on CachyOS (both use KDE Plasma on KWin Wayland).
  • They happen when the nvidia drivers (nvidia-driver-595-open) are in use, but not when the x.org nouveau driver is used.
  • They happen when monitor refresh rate is set to 300Hz, but don’t seem to happen at 60 Hz.
  • Enabling or disabling adaptive sync or HDR in the settings doesn’t seem to affect it.
  • No errors appear in the syslog at all
  • Videos playing on VLC player freeze along with the rest of the screen.
  • Audio (e.g. in VLC or firefox) keeps playing uninterrupted while the freezes happen.
  • Recording desktop with OBS results in videos where freezes aren’t visible (no dropped frames as if they didn’t happen at all)
  • There are no application crashes whatsoever

Hardware specs:
Host: Gigabyte X870E AORUS ELITE X3D
CPU: AMD Ryzen 9 9950X3D
GPU: Asus GeForce RTX 5080 ROG Astral OC
Memory: DDR5 Kingston Fury Beast 2 x 32GB
Display: Asus ROG Strix XG27ACDNG

KUBUNTU:
KDE Plasma: 6.6.4
KDE Frameworks: 6.24.0
QT: 6.10.2
Kernel: 7.0.0-22-generic (64-bit)
nvidia-driver-595-open 595.58.03

CACHYOS:
KDE Plasma 6.6.5
KDE Frameworks: 6.26.0
QT: 6.11.1
Kernel: 7.0.10-2-cachyos
nvidia 595.71.05 (later 610.43.02-1)

Any ideas what might be causing it and how to solve this? I’m suspecting it might be some power switching issue with nvidia e.g. when the GPU switches its clock frequency or the power level down, but I’m not sure. Funny thing is it doesn’t happen in CachyOS, so it can’t be a hardware issue. And why doesn’t it happen at 60 Hz? Perhaps a software issue e.g. a driver misconfiguration?

3 Likes
2

I suggest you try the -open variant of the drivers.

3

You will have to use an Ubuntu kernel with the proprietary drivers (open or not) or seek support at a CachyOS forum, we can not support this combination here (and the Ubuntu packaged driver is most likely completely incompatible with that kernel)

1 Like
4

@celticwarrior I already am using the “-open” variant of nvidia drivers, as seen from the Kubuntu specs in my first post:

KUBUNTU:
KDE Plasma: 6.6.4
KDE Frameworks: 6.24.0
QT: 6.10.2
Kernel: 7.0.0-22-generic (64-bit)
nvidia-driver-595-open 595.58.03

@ogra Excuse me? I’m not sure I understand your suggestion. CachyOS is installed on a separate SSD and has nothing to do with the Kubuntu installation. I just mentioned it because it is working fine, which points out that the culprit is likely not a hardware issue. I am not using cachyos kernel on kubuntu or vice-versa or some other combination. There are two separate and independent installations on two separate SSD’s that don’t intermix. The problem is on Kubuntu where I am getting screen freezes while the CachyOS doesn’t have them.

5

Can you try updating your driver? Looks like it’s been updated

6

OOPS!!

Mea culpa, I totally mis-read your post, ignore me :slight_smile:

7

Nope, I just installed Kubuntu 26.04 LTS on another HDD with as many default options as I could. The problem persists, so this must be present in stock Kubuntu.

  • Booted live Kubuntu 26.04 LTS USB image
  • Installed to an empty HDD with default disk layout and such
  • After installation was complete, I booted the system and fully updated it
  • Rebooted
  • Then I launched a terminal and did “sudo ubuntu-drivers install nvidia-driver-595-open”
  • Rebooted
  • Opened the System Settings // Display & Monitor and set refresh rate to 360 Hz.
  • After wiggling mouse and dragging some windows, freezes still happen.

The version of nvidia-driver-595-open is 595.71.05.

EDIT: Oops! Looks like the UEFI entry for my old Kubuntu installation on SSD is now overwritten by the new one on the HDD. Oh well, no big deal. I didn’t have anything useful on it anyway, it was just a test installation. I’ll fix it with the efibootmgr later.

8

I am experiencing the same thing with Xubuntu 26.04 LTS. Video freezes for a second or so on VLC and in youtube using Firefox. I also have an nvidia card (5060 8GB), CPU is 9950x. If I can be of any help in trying to diagnose this please let me know it is very annoying!

9

I think it could be a driver issue, possibly in combination with switching to the iGPU of your Ryzen APU, when GPU intensive work stops; if that is even a thing with an NVIDIA dGPU and an AMD iGPU.

Especially with bleeding edge hardware, the latest kernel shipping with Ubuntu, might not be enough, AFAICT the NVIDIA drivers should be the same version by now:

So only the kernel seems to be left on the driver side of things. But CachyOS, being a rolling release also has fresher KDE Plasma packages, which may contain fixes for your issues. I wouldn’t know of a way to test both systems exactly like for like. Perhaps CachyOS has some way of installing snapshot versions; think APT snapshots?

Plus, both CachyOS and Ubuntu don’t ship the upstream Linux kernel, but apply various patches; I’d wager CachyOS is doing a lot more of that than Ubuntu.

10

Oh? Are you sure the GPU is switching from nvidia to AMD and back? I originally thought this might be a P-state issue with nvidia, but I can’t really confirm it. The nvidia-smi tool shows that the GPU clock and memory clock initially surge to high values (2400 MHz // 7001 MHz), but when I stop dragging a window around, they slowly back down to their base values (255 MHz // 455 MHz, I think). This takes about 15 seconds, then the freezes start happening.

Anyway, I just installed Ubuntu 26.04 LTS (yes, the regular Ubuntu) on the hard drive by following the same steps as in my previous post. After installing nvidia-driver-595-open, rebooting and switching desktop refresh rate to 360Hz, I could not reproduce the issue. It seems to happen on Kubuntu only (notice the nvidia drivers are the same in both cases - 595.71.05).

I may try it with Xubuntu next to see, if I get the same result.

11

Do you have integrated AMD alongside NVIDIA? Some integrated AMD’s suffer freezing issues and I have been able to solve them by adding

amdgpu.dcdebugmask=0x12

To my boot options.

1 Like
12

No, I’m not, which is why I added “if that is even a thing”. :wink: I honestly don’t know how this works, but if it does (or should) work like that, it seems to match your issue.

I don’t think P-states figure in this, because those a the Perfomance states of your CPU. An easy way to check is to set the system to performance mode in the Power Profiles GUI; if the issue persists, it wasn’t anything to do with P-states.

I think @dinomonster might be right on the money. I seem to remember having read some recent-ish article on kernel development, which mentioned amdgpu.dcdebugmask=0x12 as a temporary workaround for an issue in the process of being fixed in the upstream Linux kernel; but, try as I might, I cannot remember the details or where I’ve read it.

1 Like
13

CachyOS doesn’t seem to have that line in the kernel command line.

I’ll give it a try on Kubuntu and see what happens.

But I gotta fix my bootloader EFI entry first when I have the will to do it.

14

That doesn’t have to mean much; it’s just one way of specifying module parameters directly on the command line. Cachy could be using something like a /etc/modprobe.d/ snippet to provide said parameters. Or, perhaps they have backported said patches so the parameter isn’t required anymore. Plus they are using the newer kernel to begin with.

15

I too saw this happening on my AMD-based systems (CPU AMD, GPU Nvidia) and once I changed the kernel, it never appeared again.

Now, this isn’t a solution in itself, unless you always run your own kernels, but to simply test if the 7.0.0-xx kernel release of the 26.04 base is to blame, it’s worth a shot. You could for example use one of the current mainline kernels (say 7.0.12) and see if the freezes still happen.

If not, you at least have gained an insight into which element is to blame. Once established, one would certainly have to test some more as to why the 7.0.0-xx kernel has those issues.

That finding would also explain why CachyOS behaves differently.

16

There is a slight problem with that, because the mainline kernels, while being the latest, are also unpatched, which adds another variable into the mix, because what you get with Ubuntu is actually an Ubuntu (not quite Linux) kernel, if you will. The upstream mainline kernel undergoes some patching/hardening before being delivered as Ubuntu’s kernel.

That means, it could still be an issue only present with the patched version. To exclude that possibility one should also check with the exact same unpatched version from the mainline PPA, i.e. the mainline equivalent of 7.0.0-22-generic.

1 Like
17

In my case back then, the short freezes went away with the 7.0.2 kernel, if I recall correctly. They were present with the 7.0-based Ubuntu release and with the 7.0 and 7.0.1 source code (self-compiled) ones. So my guess would be that the initial 7.0 code featured something which caused the freezes.

To my great shame, I never investigated further as the problem went away and only affected my AMD systems.

Still, if the OP has the time and motivation to check, the suggestion to alter the kernel release still stands.

1 Like
18

OK, guys, I’m back. I did some more tests, but I cannot reproduce this issue on Xubuntu 26.04 running X11 and the latest nvidia-driver-595-open driver. It seems to be a wayland thing on Kubuntu only. I’ve also tried adding the “amdgpu.dcdebugmask=0x12” to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub on my kubuntu installation. After updating grub and rebooting, I confirmed the line was present in /proc/cmdline, but unfortunately it did not solve the issue. The freezes still happen.

I see a bunch of you are recommending that I try a different kernel next. I’ll see what I can do and whether that fixes the issue.

EDIT: Which kernels exactly should I be trying out? The 7.0.0-22-generic is already installed and running (the one with problems).

apt search linux | grep linux-image

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linux-image-virtual-hwe-26.04-edge/resolute-updates,resolute-security 7.0.0-22.22 amd64
19

It definitely is happening for me on Xubuntu 26.04, the description of the symptoms are exactly what I see so I don’t think this is just a Kubuntu issue. I frequently have 2 firefox windows open in the screen at once each taking up half of my screen (2560x1440) and can make the stutters/freezes happen pretty regularly by opening new tabs, or scrolling through my favourites in one of the browsers. Sometimes the pauses are several seconds long.

I also have Xubuntu 26.04 installed on another Intel machine (245k) with integrated graphics and I can’t get it to stutter by opening new tabs / scrolling though my favourites no matter what I do which discounts Firefox as the problem.

20

I also had this same issue on Kubuntu 26.04, as a repeating nuisance it had a very bad impact on usability.

Immediate usability issue is fixed simply by downgrading to Kubuntu 25.10. It currently uses kernel version 6.17.0-35-generic which seems to be unaffected by this issue.

Specs:

  • ASUS Tuf B850-plus wifi
  • Ryzen 7 7800x3D
  • 16GB ddr5 6000 cl30
  • Asus Tuf rx 9070 xt