Bug 509674

Summary:	Content with refresh rates lower than the display's suffers from consistent dropped frame issues
Product:	[Plasma] kwin	Reporter:	fililip <team>
Component:	platform-drm	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	CONFIRMED ---
Severity:	normal	CC:	akselmo, nate, team, xaver.hugl
Priority:	NOR
Version First Reported In:	6.4.90
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	Judder comparison with overlays enabled vs disabled result

Description fililip 2025-09-19 11:01:03 UTC

Created attachment 185086 [details]
Judder comparison with overlays enabled vs disabled

SUMMARY
Playing a video (or playing a game) with overlay planes enabled causes said content to consistently drop every other frame when its refresh rate is below the display's (ie 60 FPS content on a 120Hz display). Making it fullscreen or keeping it windowed does not change the outcome, same goes for HDR/color profile on/off.

STEPS TO REPRODUCE
1. Set the display's refresh rate to 120Hz
2. Download this video with yt-dlp (-f 299, 1080p format) https://www.youtube.com/watch?v=RgGwWN9EC8g
3. Play it in mpv with vo=dmabuf-wayland
4. Make it fullscreen or windowed
5. Take a picture of it with a camera

OBSERVED RESULT
The video judders (some 'blocks' are brighter than others)

EXPECTED RESULT
The video is played back smoothly (every 'block' is similarly bright, maybe with the exception of the first and last ones)

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.4.90
KDE Frameworks Version: 6.18.0
Qt Version: 6.10.0
Kernel Version: 6.16.7-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 20 × AMD Ryzen AI 9 365 w/ Radeon 880M
Memory: 32 GiB of RAM (27.2 GiB usable)
Graphics Processor: AMD Radeon 880M Graphics

ADDITIONAL INFORMATION
Playing that video in a browser (that VSyncs to the max refresh rate) does not cause the issue. If this ends up being an amdgpu bug, I'll report it there. I've attached a comparison to illustrate the issue better.

Comment 1 fililip 2025-09-19 11:50:37 UTC

I should add that VRR needs to be disabled to test this correctly (my laptop does not have a VRR-capable display).

Additionally, syncing the screen with an external app constantly updating at 120Hz (like simply running vkcube in the background) makes this issue go away.

Comment 2 fililip 2025-09-19 17:02:16 UTC

It appears that even VRR is completely broken with overlays + mpv on my PC with an RDNA2 card. I had to disable night light and disconnect my secondary display to start to see random refresh rate jumps with that same 60fps video, even with fullscreen vo=gpu-next. Other apps (GL/Vulkan) seem to work fine so far with VRR though, this could be some kind of mpv + overlay problem.

Things like switching the active application introducing stutter that wasn't there without overlays are also present; I guess there are still issues with amdgpu to sort out. :(

Comment 3 Akseli Lahtinen 2025-09-24 08:47:12 UTC

Created attachment 185206 [details]
result

I admit I didn't really understand much.. :') But is this the expected result? If so, I can't reproduce the bug.

Operating System: Fedora Linux 42
KDE Plasma Version: 6.5.80
KDE Frameworks Version: 6.19.0
Qt Version: 6.9.2
Kernel Version: 6.16.7-200.fc42.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 12 × AMD Ryzen 5 3600 6-Core Processor
Memory: 16 GiB of RAM (15.5 GiB usable)
Graphics Processor: AMD Radeon RX 6600

Comment 4 Akseli Lahtinen 2025-09-24 08:47:37 UTC

(In reply to Akseli Lahtinen from comment #3)
> Created attachment 185206 [details]
> result
> 
> I admit I didn't really understand much.. :') But is this the expected
> result? If so, I can't reproduce the bug.
> 
> Operating System: Fedora Linux 42
> KDE Plasma Version: 6.5.80
> KDE Frameworks Version: 6.19.0
> Qt Version: 6.9.2
> Kernel Version: 6.16.7-200.fc42.x86_64 (64-bit)
> Graphics Platform: Wayland
> Processors: 12 × AMD Ryzen 5 3600 6-Core Processor
> Memory: 16 GiB of RAM (15.5 GiB usable)
> Graphics Processor: AMD Radeon RX 6600

To add, my refresh rate is 165hz

Comment 5 fililip 2025-09-24 12:23:45 UTC

You need to ensure nothing gets constantly painted except for the video in mpv. Running additional software which vsync itself will work around this bug.

Comment 6 Zamundaaa 2025-10-08 12:33:15 UTC

Can confirm, when doing multi gpu testing I saw the frame graph of (very slow) eglgears_wayland being way smoother while moving the cursor. Not sure what could cause it yet, but something's definitely wrong.