Bug 504686 (Omar)

Created attachment 181669 [details]
Screenshot of my KDE display settings

SUMMARY
Hi folks! I have been using CachyOS with KDE Plasma for about a year. For info, I am currently using the latest version of CachyOS with the latest mesa-git, lib32-mesa-git, linux-cachyos-rc and linux-cachyos-rc-headers packages, and I am running into an issue while on the latest stable KDE which I have been experiencing for a few weeks now (3-4 weeks I think). This issue occurs even on a fresh install as tested. My monitor is a 3440x1440 175hz HDR Oled Dell model with GSync. My GPU is an AMD 9070XT that I got on launch.

The issue is when using Adaptive Sync on "Automatic", I am noticing that when I go full-screen while watching a YouTube video on Firefox or when I play a game on Steam that I can get very low refresh rate and low FPS. This doesn't happen all the time, but maybe 60 percent of the time. I have a feeling that this might be something to do with the KWIN compositor, but I could be wrong.

The reason why I think that is because I used the "Show FPS" options in the KDE Desktop Effects settings menu, and a graph spawned in the top-right. The graph stays there all the time, and while it's ON, I don't encounter the issue above at all as the compositor is on the whole time. I tested this in combination with the "Show Compositing" option in the same settings menu while turning "Show FPS" off, and as soon as I go to a YouTube video, go Full-screen, wait for my cursor to go away as I only see the video, the video's FPS hiccups for a sec, and then I either see a smooth video feed OR I see a very juddery experience where the refresh rate goes down to about 13 hz immediately and stays there until the compositor turns back on (when I start moving the mouse as the cursor renders back in). The smoothness doesn't come back all the time though as sometimes I would be stuck with the same 13hz/13fpz juddery experience for the entirety of my desktop experience as my mouse and everything being rendered on screen (even if just on my Desktop) runs at 13fps until I toggle HDR ON or OFF.

It gets fixed temporarily when I do that until the issue repeats randomly when entering full-screen and the compositor turns off. I can only fix this either by toggling HDR ON or OFF from my testing. Changing the Adaptive Sync option to "Always" or "Never" doesn't fix it. Funny enough, when this issue stated above occurs, and I try to set Adaptive Sync to "Never", the refresh rate still fluctuates and goes to around 13 hz, so it seems that VRR is still active but broken?

Also, this issue can start regardless of whether or not I am using HDR ON in the KDE settings. A system restart also fixes this temporarily until the issue happens. I used Firefox and a YouTube video to demonstrate this issue below, but this issue occurs in full-screen games as well which is unfortunate as it renders the experience unusable. 

Another reason why I think this might be the KWin compositor at fault OR maybe KWin + Mesa at fault is that when I used Gamescope or ChimeraOS's gamescope-steam-session to play Steam games using the Gamescope compositor, I never experienced the issue mentioned in this report at all after a long playtime. 

STEPS TO REPRODUCE
1. Turn Adaptive Sync to "Automatic"
2. Go to Firefox (not sure about other browsers) and play a YouTube video in full-screen or open any full-screen game.
3. Wait till your mouse cursor disappears.
4. You will now see a hiccup as the compositor turns off, and you will then either see a smooth video feed OR you will see your refresh rate go down very low (in my case around 13 hz) as the video's FPS goes. I am assuming because VRR is active, the video's FPS goes does really low, and then the monitor's GSYNC matched the refresh rate to that FPS.
5. Move the mouse, and you will see another hiccup as the compositor kicks back in and you will either see a smooth video feed OR you will see the desktop experience gets affected by the same low FPS/Hz issue.

OBSERVED RESULT
Fairly often low/sporadic/fluctuating FPS and monitor refresh rate while Adaptive Sync is "Automatic" and the KWin compositor is off when viewing a full-screen video or playing a full-screen game.

EXPECTED RESULT
The FPS and refresh rate of my monitor should be at it's maximum that the GPU can render especially when the CPU is not being taxed.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: CachyOS with the latest mesa-git, lib32-mesa-git, linux-cachyos-rc and linux-cachyos-rc-headers packages.
KDE Plasma Version: 6.3.5 (& 6.3.90 tested/issue persists)
KDE Frameworks Version: 6.14.0
Qt Version: 6.9.0

ADDITIONAL INFORMATION
For video evidence of the issue, I wasn't able to attach the videos here as they were over the size limit, but they can be viewed here (https://www.reddit.com/r/cachyos/comments/1ksdpll/vrr_breaks_after_going_fullscreen_in_kde/) in the reddit post I made in the CachyOS subreddit. Please have a look if possible. Thank you.