https://bugs.kde.org/show_bug.cgi?id=527224
Bug ID: 527224
Summary: Periodic frame hitch at 15Hz on 180Hz output when a
165Hz is also active (NVIDIA, Wayland)
Classification: Plasma
Product: kwin
Version First 6.8.0
Reported In:
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: platform-drm
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
Created attachment 197202
--> https://bugs.kde.org/attachment.cgi?id=197202&action=edit
weston-simple-egl output, followed by partial Firefox output, separated by a
bunch of blank newlines
DESCRIPTION
With two monitors at 180Hz and 165Hz, native Wayland clients on the 180Hz
monitor get a frame-timing hitch exactly every 66.7 ms (= 1 / (180-65) ). I
noticed this due to Firefox being slightly stuttery, but it is not a
Firefox-specific issue, and does not occur outside kwin.
I imagine the same problem applies to all multi-refresh-rate setups.
The following actions make it go away:
- Disabling the 165Hz monitor
- Enabling VRR on the 180Hz monitor
- Setting the 180Hz monitor to run at 165Hz
STEPS TO REPRODUCE
1. Two DisplayPort monitors, one at 180Hz and one at 165Hz, both enabled, VRR
off.
2. Ensure Firefox is setup to run as a native Wayland client
3. On the 180Hz monitor, run WAYLAND_DEBUG=1 firefox 2>&1 | grep
'wl_callback.*done' and scroll a page
4. Alternatively run WAYLAND_DEBUG=1 weston-simple-egl 2>&1 | grep
'wl_callback.*done'
OBSERVED RESULT
Firefox frame callbacks occur at a distance of 5-6ms from each other, but every
~12 callbacks a timestamp is duplicated and followed by an ~11–12ms gap. The
hitches occur at a 66.7ms period, i.e. 15Hz, i.e. the frequency difference
between 180Hz and 165Hz.
The same happens in weston-simple-egl.
EXPECTED RESULT
Frame callbacks on the 180 Hz output at a steady 5.56 ms, unaffected by the
second output.
SOFTWARE/OS VERSIONS
Operating System: Arch Linux (fully updated)
KDE Plasma Version: 6.8.0. This also occurred on 6.7; I only got around to
reporting it now.
KDE Frameworks Version: 6.31.0
Qt Version: 6.12.0
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