https://bugs.kde.org/show_bug.cgi?id=527500
Bug ID: 527500
Summary: Since 6.8.0: after resuming a paused Vulkan video
(NVIDIA), the picture stays frozen for as long as it
was paused
Classification: Plasma
Product: kwin
Version First 6.8.0
Reported In:
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
Created attachment 197416
--> https://bugs.kde.org/attachment.cgi?id=197416&action=edit
Freeze logs, stacks and Wayland trace
SUMMARY
Since the upgrade from KWin 6.7.5 to 6.8.0, mpv (vo=gpu-next, gpu-api=vulkan)
on NVIDIA freezes after I
resume a paused video: audio keeps running, the picture stays stuck, then it
jumps ahead with a burst of
dropped frames. The freeze lasts almost exactly as long as the video was
paused. Moving the mouse can end it
early. Nothing else in the graphics stack changed at the same time (NVIDIA
615.78.08 since 2026-10-12,
mpv 0.41.0 and libplacebo unchanged).
STEPS TO REPRODUCE
1. Play a video fullscreen in mpv with --vo=gpu-next --gpu-api=vulkan (default
FIFO present mode), NVIDIA GPU.
2. Pause it (seen after pauses from 7 s to 154 s).
3. Resume.
It does not happen on every resume, only sometimes. In 4 days of normal use I
logged 7 freezes of this
kind, plus 3 right after a video started. I have not found what makes one
resume freeze and another not.
OBSERVED RESULT
The picture stays frozen after resuming for about as long as the pause lasted.
Pause vs freeze length from my
log: 7 s -> 6.8 s, 53 -> 52.7, 112 -> 111.3, 24 -> 23.8, 59 -> 59.1, 102 ->
100.1, 154 -> 154.0.
While frozen, mpv's video output thread is blocked in drmSyncobjTimelineWait
(libnvidia-glcore, called from
libplacebo), waiting for a buffer release. 16 such freezes logged from
2026-10-17 to 2026-10-20; none of this
shape in the same log for 2026-10-06 to 2026-10-15 (KWin 6.7.5).
EXPECTED RESULT
Playback continues immediately after resuming.
WHAT I FOUND
KWin 6.8.0 is the first version here that advertises
wp_commit_timing_manager_v1. The NVIDIA Vulkan WSI uses
it on every commit. On the first commit after a pause it sends a stale target:
previous target + one refresh,
i.e. as far in the past as the pause was long (the presented events from before
the pause are only dispatched
at resume). On a nested "kwin_wayland --virtual" this does not freeze; on the
real DRM output it freezes for
the length of the pause. With --vulkan-swap-mode=mailbox the WSI sends no
commit timestamps at all.
Details, stacks and a Wayland trace are in the attached attachment-logs.txt.
SOFTWARE/OS VERSIONS
Operating System: CachyOS Linux
KDE Plasma Version: 6.8.0
KDE Frameworks Version: 6.31.0
Qt Version: 6.12.0
Kernel Version: 7.2.10-1-cachyos (64-bit)
Graphics Platform: Wayland
Graphics Processor: NVIDIA GeForce RTX 4080 SUPER, driver 615.78.08
(nvidia-open)
mpv 0.41.0, libplacebo 7.360.1
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