https://bugs.kde.org/show_bug.cgi?id=431707
Bug ID: 431707
Summary: setting new latency option to balance or other options
even more in favor of latency causes frame drops in
gaming on Wayland
Product: kwin
Version: git master
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: compositing
Assignee: kwin-bugs-n...@kde.org
Reporter: tempel.jul...@gmail.com
Target Milestone: ---
SUMMARY
When there is high GPU load by games and vsync is enabled for them (which seems
to be a must on Wayland to prevent stutter, either fifo or mailbox mode),
latency options with lower latency than "prefer smoother animations" cause
frame drops. Manually setting "prefer smoother animations" each time a game is
played is rather inconvenient and it also seems to have higher input lag than
on Xorg with suspended compositing and vsync done entirely by the game.
STEPS TO REPRODUCE
1. Start Plasma Wayland and leave latency option at "balanced" or set it even
more aggressive in favor of lower latency.
2. Start a game with vsync that has high GPU load (e.g. super sampling via
configurable resolution scale in Hitman 2) and watch fps and frame time graph
via Mangohud.
OBSERVED RESULT
There are dropped frames and thus stuttering/reduced performance with the
aforementioned latency options, whereas "prefer smoother animations" shows
normal performance (with higher input lag than on Xorg with suspended
compositing though):
https://invent.kde.org/plasma/kwin/uploads/fe965708e03d4b86ce535a1a9bb29dff/Screenshot_20210115_142349.png
https://invent.kde.org/plasma/kwin/uploads/6d1aba27cd85f6ecf4e7fadda8864f25/Screenshot_20210115_142316.png
EXPECTED RESULT
Ideally, games on Wayland in fullscreen should work as good as on Xorg with
automated suspending of compositing, i.e. without any frame drops and
additional input lag by compositor vsync.
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch 5.10
KDE Plasma Version: kwin git-master v5.19.90.r466.g2d1994e06
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