After upgrading from KDE Plasma 6.5.5 to 6.6.0, the Wayland session became noticeably sluggish on a laptop with Intel integrated graphics (no discrete GPU). The issue persists through 6.6.3. Downgrading only the `kwin` package to 6.5.5-3 while keeping all other Plasma 6.6 components at 6.6.x immediately resolves the problem. SYMPTOMS - Noticeable delay (~0.5s) when opening the application launcher - Laggy mouse cursor movement during desktop interactions - Input lag when typing in KRunner - CPU spikes when interacting with Plasma shell components (System Settings, lock screen, Spectacle) - Fan spinning more frequently than on 6.5.5 - General sluggishness across all Plasma shell UI, though native applications (browsers, terminals) are less affected REPRODUCTION STEPS 1. Run Plasma 6.6.x on Wayland with an Intel iGPU-only system 2. Observe lag when opening the app launcher, using KRunner, or interacting with System Settings 3. Downgrade only `kwin` to 6.5.5-3: `sudo pacman -U /var/cache/pacman/pkg/kwin-6.5.5-3-x86_64.pkg.tar.zst` 4. Log out and back in 5. Observe that all lag is gone WHAT I EXPECTED Same smooth, responsive desktop experience as Plasma 6.5.5 on Wayland. WHAT HAPPENED Desktop interactions became sluggish with delayed input response and visible CPU spikes, specifically tied to KWin 6.6. KEY OBSERVATIONS: - KWin-specific: Downgrading only `kwin` to 6.5.5 resolves the issue. All other Plasma components remain at 6.6.x. - Wayland-only: Logging in to an X11 session does not exhibit the problem. - Not Flatpak-related: The issue occurs with no Flatpak apps installed or running. (See related bug #516721, which describes a possibly separate Flatpak-specific variant.) - Not configuration-related: The issue occurs on a fresh user account. - Persists through 6.6.3: Tested on 6.6.0 and confirmed still present as of 6.6.3. SYSTEM INFORMATION ``` Operating System: Arch Linux KDE Plasma Version: 6.6.0 (regression present through 6.6.3) KDE Frameworks Version: 6.23.0 Qt Version: 6.10.2 Kernel Version: 6.18.9-arch1-2 (64-bit) Graphics Platform: Wayland Processors: 8 × Intel® Core™ i5-8350U CPU @ 1.70GHz Memory: 8 GiB of RAM (7.6 GiB usable) Graphics Processor: Intel® UHD Graphics 620 ``` **No discrete GPU present. Intel iGPU is the only graphics adapter.** OTHER AFFECTED USERS This regression has been reported independently by multiple users across different distributions and hardware: - EndeavourOS, Intel i5-8350U / UHD 620 (this report) - Fedora 43, Intel Core Ultra 5 125H / Intel Arc iGPU - KDE Neon, AMD Ryzen (related bug #516721) - Arch Linux, various hardware (EndeavourOS forum thread: https://forum.endeavouros.com/t/issues-after-plasma-6-6-update/78216) - KDE Discuss thread: https://discuss.kde.org/t/higher-cpu-use-since-plasma-6-6/44565 All reporters confirm the issue is resolved by downgrading KWin to 6.5.x. SEE ALSO - Bug #516721 — Performance regression in KWin when using Flatpak (related but distinct; this bug occurs without Flatpak) - Bug #516240 — QAnimationDriver fix in 6.6.1 (did not resolve this issue)
Please attach the output of > wayland-info and > journalctl --user-unit plasma-kwin_wayland --boot 0 It sounds as though your system may be falling back to software rendering for some reason.
Created attachment 191933 [details] wayland-info
I also have this bug. I’m using KDE Neon. My entire system is slow — the menu, browser, typing at times, applications… This is my setup: Operating System: KDE neon User Edition KDE Plasma Version: 6.6.4 KDE Frameworks Version: 6.25.0 Qt Version: 6.10.2 Kernel Version: 6.8.0-110-generic (64-bit) Graphics Platform: Wayland Processors: 12 × Intel® Core™ i7-8750H CPU @ 2.20GHz Memory: 64 GiB of RAM (62.6 GiB usable) Graphics Processor 1: Intel® UHD Graphics 630 Graphics Processor 2: NVIDIA GeForce RTX 2060 Manufacturer: Micro-Star International Co., Ltd. Product Name: GS75 Stealth 8SE System Version: REV:1.0 Attached are text files with my wayland-info and journalctl logs in case they are useful.
Created attachment 191934 [details] journalctl --user-unit plasma-kwin_wayland --boot 0
Good, that looks exactly like bug 517987 *** This bug has been marked as a duplicate of bug 517987 ***
Hi, this might be the same bug, but I'd like to add I'm not on Nvidia like the other commentor here are. I will not be able to post the outputs of the commands you requested until Monday as I don't have access to the affected laptop currently.
Created attachment 192018 [details] wayland info
Created attachment 192019 [details] journalctl --user-unit plasma-kwin_wayland --boot 0
These are my logs, I don't see anything particularly obvious here
Yeah, nothing suspicious there. Judging by the wayland-info output, KWin is using the GPU. Please get the output of > WAYLAND_DEBUG=1 systemsettings 2>&1 | grep dmabuf and also check the "plasma renderer" (search for it in krunner) for whether or not it's set to a software renderer, and whether or not setting the rendering backend explicitly to OpenGL (and rebooting afterwards) helps
WAYLAND_DEBUG=1 systemsettings 2>&1 | grep dmabuf [2077283.735] {Default Queue} wl_registry#2.global(57, "zwp_linux_dmabuf_v1", 5) [2077303.384] wl_registry#42.global(57, "zwp_linux_dmabuf_v1", 5) [2077303.387] -> wl_registry#42.bind(57, "zwp_linux_dmabuf_v1", 3, new id [unknown]#44) [2077303.429] -> zwp_linux_dmabuf_v1#44.destroy() [2077303.769] wl_registry#43.global(57, "zwp_linux_dmabuf_v1", 5) The plasma renderer was set to Automatic, changing to OpenGL and restarting did not help
Created attachment 192241 [details] GPUTOP KDE 6.5.5
Created attachment 192242 [details] GPUTOP KDE 6.6.5
Created attachment 192244 [details] GPUTop 6.6.5
Created attachment 192245 [details] GPUTop 6.5.5
I noticed gputop shows very different applications running on 6.6 and 6.5, plasma is missing aswell as my terminal emulator, both of these feel laggy, while vivaldi which isn't missing works fine.
After more investigation, it turns out I was running `mesa-amber`. I switched to it at some point in early 2025 to work around an unrelated bug that's apparently long since fixed. Reinstalling regular `mesa` makes plasmashell show up on the GPU again and the stuttering is gone. For anyone finding this later: on Intel UHD CometLake-H (Gen 9.5, i915) under kwin 6.5, plasmashell was rendering on the GPU via mesa-amber's classic `i965_dri.so` driver, which still supports Gen 9.5 hardware. Under kwin 6.6 plasmashell logs `Failed to query DMA-BUF formats`, holds no `/dev/dri/*` FDs, loads `swrast_dri.so`, and renders in software via `wl_shm`, hence the stutter. I haven't dug into exactly what changed in the negotiation between 6.5 and 6.6, but with proper mesa (iris) it's a non-issue. Not really worth a fix on the kwin side since mesa-amber on Gen 9.5 hardware is the wrong stack to begin with, happy to close. Leaving the explanation here in case the next person to hit this finds it.
Ah, in that case this is https://gitlab.freedesktop.org/mesa/mesa/-/work_items/13396