https://bugs.kde.org/show_bug.cgi?id=524033
Bug ID: 524033
Summary: Kwin Wayland is too jittery compared to Xorg
Classification: Plasma
Product: kwin
Version First 6.7.4
Reported In:
Platform: Arch Linux
OS: Linux
Status: REPORTED
Keywords: wayland-only
Severity: major
Priority: NOR
Component: performance
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
DESCRIPTION
KDE desktop is moving to Wayland only and will move away from X11 future
versions, but Kwin as a standalone compositor has a major issue that Xorg
don't: Performance. Despite having higher average FPS in 3D applications/games
with Kwin Wayland, I have high amount of stutter/frame skip, including mouse
cursor, when interacting with Kwin.
I listed below some situations where Kwin struggles:
STEPS TO REPRODUCE
* When using native Wayland applications which uses CPU rendering such as Kate,
Dolphin, Konsole, Kwin is very jittery and the workaround is to launch
application with Xwayland with QT_QPA_PLATFORM=xcb. I previously opened a bug
about this issue (https://bugs.kde.org/show_bug.cgi?id=513295), but it was
closed without being solved and tested.
* Kwin also stutters when cursor shape changes
(https://bugs.kde.org/show_bug.cgi?id=509669).
* Opening display settings and clicking on "Identify screens" freezes Kwin for
~500 ms.
* Opening tab box with ALT+TAB also freezes Kwin for ~500 ms the first time
(https://bugs.kde.org/show_bug.cgi?id=479250).
* Moving a window the edges of a screen freezes Kwin for ~300 ms the first
time.
* Here is an example of user complaining about cursor lags using JetBrains
Toolbox:
https://youtrack.jetbrains.com/projects/JBR/issues/JBR-10036/Wayland-system-cursor-stutter-freezing
I applied to following patch on the top of Kwin to see when it hangs more than
100 ms:
```
--- a/src/backends/drm/drm_gpu.h
+++ b/src/backends/drm/drm_gpu.h
@@ -74,7 +74,7 @@ public:
/**
* This should always be longer than any real pageflip can take, even with
PSR and modesets
*/
- static constexpr std::chrono::milliseconds s_pageflipTimeout =
std::chrono::seconds(1);
+ static constexpr std::chrono::milliseconds s_pageflipTimeout =
std::chrono::milliseconds(100);
DrmGpu(DrmBackend *backend, int fd, std::unique_ptr<DrmDevice> &&device);
~DrmGpu();
```
And after I applied this patch, I saw the message "The main thread was hanging
temporarily!" many times even on normal desktop usage with an AMD Ryzen 7 3700X
CPU and a Nvidia GeForce RTX 2080 SUPER which are high end hardware from 2019.
With Xorg, even on a old laptop from 2009 with an Intel Core 2 Duo and GeForce
9600M GT, the cursor doesn't drop a single frame.
OBSERVED RESULT
Kwin is jittery and freezes.
EXPECTED RESULT
Kwin render smoothly.
The cursor shouldn't drop any frame.
SOFTWARE/OS VERSIONS
KDE Plasma Version: 6.7.4
KDE Frameworks Version: 6.28.0
Qt Version: 6.11.1
Linux 7.1.6-arch1-1
ADDITIONAL INFORMATION
When my Nvidia GPU hangs due to a context switch timeout, I can still move the
cursor but when the cursor shape changes by hovering a link for example, the
cursor doesn't move anymore and the keyboard become unresponsive (Capslock LED
is stuck) and I have "The main thread was hanging temporarily!" and not
"Pageflip timed out! This is a bug in the nvidia_drm kernel driver", which
means this is a Kwin issue and not an issue with the display driver which is
still responding to atomic commits. On Xorg and GNOME Wayland, I can still move
the cursor in the same situation.
--
You are receiving this mail because:
You are watching all bug changes.
