I'm experiencing strange performance issues when using KWin + Desktop Effects + VSync (suspending of desktop effects is disabled). I'm not sure how to describe it correctly, but sometimes it looks like the framerate is really low (around 20fps), despite that various framerate counters may show 160+ fps. The worst thing about it, I cannot reliably reproduce it, most of time the picture is nice and smooth, but sometimes the "visual" framerate would drop for a few seconds and then restore. Switching window focus usually restores the performance. I've also noticed it's somehow related to system's uptime, the longer it runs, the higher is chance to hit the problem. But it's not necessary, sometimes it starts just after boot. It's very annoying, especially if you're playing video games, or watching 60fps videos. There is no framerate drops if I disable VSync, enable desktop effects suppression, or use another window manager, so my guess it that frames get dropped somewhere in the composition pipeline. Hardware: AMD RX480 with amdgpu X driver & Mesa OS: openSUSE 42.3 with Plasma 5.8 Currently, I have Mesa-git, but the problem is also reproducible with Mesa 17.1 I'd like to provide more information, but I don't know what you may need.
Created attachment 107709 [details] KWin support information
please watch your dmesg output and maybe xorg log for whether there are infos like "hung gpu"
Nothing abnormal in dmesg and Xorg.log. Some advanced games do produce GPU VM FAULTs on start, but it's hardly related to the problem.
you could try enabling the showfps effect. One of it's side effects is that it triggers constant repaints. Thus a stutter in the compositing engine would be noticeable. Right now it could be e.g. the applications performing a stutter or the compositor.
I've been using the 'showfps' effect for some time now, and it looks like stutter does not happen if you have it enabled. However, I've noticed that with vulkan apps and unigine superposition benchmark KWin's framerate is half of framerate of application. E.g., if in Talos Principle you have 90 fps, you'll get 45 in kwin's showfps effect, and it actually feels like you have 45 fps. There is no difference if you have Vsync enabled or disabled. Should I report another bug for that?
Another random observation: on long uptimes minimizing & restoring windows causes stutter. Killing and restarting plasmashell fixes it.
(In reply to network723 from comment #5) > E.g., if in > Talos Principle you have 90 fps, you'll get 45 in kwin's showfps effect, and > it actually feels like you have 45 fps. KWin never renders faster than your screen, which is at 60 Hz. If an app renders at 90 Hz, KWin will restrict it to the refresh rate of the screen. More is just physically not visible anyway. It might be that the system is under stress and due to that KWin is not able to render at 60 Hz.
>It might be that the system is under stress and due to that KWin is not able to render at 60 Hz. Well, I you run the same application in OpenGL mode, KWin would show you 60Hz even if framerate of the application drops to 20Hz. Radeontop shows 100% gpu utilization in both cases. But like I said, it was a random observation, GPU-heavy vulkan apps is not something I use daily, while random can stutters happen in any opengl program while you have KWin's VSync enabled.
This sounds like it may be a duplicate of this bug: https://bugs.kde.org/show_bug.cgi?id=344433 Maybe try out if setting KWIN_TRIPLE_BUFFER=0 helps.
This issue report is quite old. Can you please confirm, that it still persists with KDE 5.23?
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This bug has been in NEEDSINFO status with no change for at least 30 days. The bug is now closed as RESOLVED > WORKSFORME due to lack of needed information. For more information about our bug triaging procedures please read the wiki located here: https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging Thank you for helping us make KDE software even better for everyone!