I build all KDE stuff from git master every day, and for at least the last two days, kwin_wayland has been consuming between 20 and 60% of a CPU core at idle. It causes input lag and makes the system nearly unusable. I attempted to bisect but was unable to due to tight coupling between KWin and its dependencies. The journal log doesn't have anything fishy-looking in it. I'm not sure how to debug this but can provide any logs.
kwin_x11 is unaffected. I've temporarily gone back to X11 to have a usable system.
This seems to have been fixed with a mesa update today.
Never mind, it turned out that that didn't fix it. However, after some investigation in #kwin, setting `KWIN_DRM_NO_AMS=1` *did* fix it. So it looks like this isue is related to eprformance issues with the AMS cursor. Re-opening.
(In reply to Nate Graham from comment #3) > Never mind, it turned out that that didn't fix it. > > However, after some investigation in #kwin, setting `KWIN_DRM_NO_AMS=1` > *did* fix it. So it looks like this isue is related to eprformance issues > with the AMS cursor. Re-opening. I am also impacted by this. Nate's workaround seems to work for me. Note that previous to the workaround, in addition to the CPU consumption from kwin_wayland, I was unable to create new desktops and switch between existing desktops using the overview effect. The workaround seems to have fixed that issue as well.
A possibly relevant merge request was started @ https://invent.kde.org/plasma/kwin/-/merge_requests/1904
A possibly relevant merge request was started @ https://invent.kde.org/plasma/kwin/-/merge_requests/1907
Git commit 50c167c94b33702f3f026e007bda424ec1af047d by Xaver Hugl. Committed on 19/01/2022 at 10:31. Pushed by zamundaaa into branch 'master'. backends/drm: fix reallocation check When no modifiers are used at all, we shouldn't check them. M +2 -1 src/backends/drm/egl_gbm_backend.cpp https://invent.kde.org/plasma/kwin/commit/50c167c94b33702f3f026e007bda424ec1af047d
Git commit 547bb52c6c3833d76bbffef46fa9b3f3ae51dccf by Vlad Zahorodnii, on behalf of Xaver Hugl. Committed on 19/01/2022 at 17:25. Pushed by vladz into branch 'Plasma/5.24'. backends/drm: fix reallocation check When no modifiers are used at all, we shouldn't check them. (cherry picked from commit 50c167c94b33702f3f026e007bda424ec1af047d) M +2 -1 src/backends/drm/egl_gbm_backend.cpp https://invent.kde.org/plasma/kwin/commit/547bb52c6c3833d76bbffef46fa9b3f3ae51dccf
That completely fixes the problem for me, hooray! kwin_wayland is once again down to 0% CPU most of the time, with occasional spikes to 10%.
Do you know if these changes are already in KDE Neon Testing?