https://bugs.kde.org/show_bug.cgi?id=520443
--- Comment #11 from [email protected] --- Im out of ideas, so went with ChatGPT. Not sure if it's helpful, but here it is: Title: KWin Wayland screencast causes frametime stutter in games when a PipeWire screencast session is active Summary Starting a Wayland screencast through KWin causes noticeable frametime stutter in games, even before recording or streaming begins. The issue appears as soon as a monitor or window is selected for capture. This affects multiple applications using the PipeWire desktop capture portal and does not appear to be application-specific. Environment Distribution: Manjaro Linux KDE Plasma: 6.6.5 KWin: 6.6.5 (Wayland) Qt: 6.11.1 Kernel: Linux 6.18.36 Mesa: 26.1.2 GPU: AMD Radeon RX 9070 XT (RDNA4, radeonsi) PipeWire server: 1.6.6 xdg-desktop-portal-kde: (latest Manjaro package) Hardware AMD Radeon RX 9070 XT Three monitors (also reproduced with only one monitor connected) All displays running at approximately 60 Hz Adaptive Sync is not supported on any connected display. Description Whenever a PipeWire screencast session is started through KWin, games immediately begin exhibiting frametime stutter. The stutter starts as soon as the capture source is selected. Recording or streaming does not need to begin. Average FPS remains largely unchanged, but frametime becomes uneven enough to produce visible microstutter during gameplay. The issue is reproducible regardless of whether the capture source is: Entire screen Single monitor Individual window Game window The issue occurs in every game tested. Applications tested The issue occurs with multiple applications using the Wayland desktop capture portal: OBS Studio Discord screen sharing Because multiple independent applications reproduce the same behavior, this does not appear to be application-specific. Comparison with vkCapture Using vkCapture (game capture) does not introduce any frametime stutter. Games remain perfectly smooth while being captured through vkCapture. This suggests that the rendering pipeline itself is functioning correctly and that the issue is specific to KWin's desktop screencast implementation. Troubleshooting performed The following changes had no effect: Disabled fractional scaling (all displays at 100%) Disabled two monitors (tested with a single display) Tested monitor capture, window capture and game window capture Tested OBS and Discord Verified that PipeWire negotiates DMA-BUF successfully (no SHM fallback) Adaptive Sync is unavailable Vulkan FIFO (vsync) is used, but this does not affect vkCapture PipeWire negotiation PipeWire successfully negotiates DMA-BUF modifiers. Example: Modifier: 0x200000000082305 Stream state: streaming No PipeWire errors are reported during normal operation. Expected result Starting a PipeWire screencast should not affect frametime stability of running games. Actual result As soon as the screencast session becomes active, games begin exhibiting consistent frametime spikes and visible microstutter. Additional notes This appears to affect the KWin screencast path rather than PipeWire itself. Since the issue reproduces with multiple applications (OBS and Discord), while vkCapture remains unaffected, it seems likely that the problem lies somewhere in the KWin screencast implementation or its synchronization with the graphics driver. If additional debug logs or traces would be useful, I would be happy to provide them. -- You are receiving this mail because: You are watching all bug changes.
