Version: unspecified (using KDE 4.4.4) OS: Linux Subj. With compositing enabled — http://img517.imageshack.us/img517/6811/128np.png and with disabled — http://img13.imageshack.us/img13/6235/126p.png Reproducible: Always
this is no bug but an architetural limit - and not in the windowmanager :-( a) it's likely (partially...) more related to the framerate than to the fact of another GL client b) nevertheless, the driver needs to manage/swap between 2 gl contexts - what can be slow c) it's also necessary to convert the X drawables into textures, what can be slow (depending on the driver again) as well (afaics the css nvidia driver shows best results on this so far, unlimited GL application will stress the GPU, but hardly the CPU here, neither in kwin nor in X11) the minimum information you need to provide is your GPU & driver as well as the settings in the advanced tab of "kcmshell4 kwincompositing" in order to check the impact of the second GL context you can limit the framerate of the gl application (eg. all x screensaver hacks provide a "-delay" flag (40000 will result in 24-25fps) and on the other hand run a video with the same framerate and of comparable size (eg. in mplayer "-fps") there will however always be an overhead and it's heavier on the GL backend than on the XRender backend.
GPU is nvidia 9500gt with nvidia (256.35) driver. Kwin uses next settings: Compositing type: OpenGL OpenGL mode: texture from pixmap Texture filter: Trilinear With enabled direct rendering. The same situation is with blu-ray videos. When I watching 1080p in mplayer and compositing is disabled — I've got 10-15% of CPU usage, but if compositing is enabled — CPU usage increases to 70-80% (60-70% falls on Xorg)... http://img638.imageshack.us/img638/8697/132u.png P.S. Maybe I'm sending too many reports, sorry if that :)
(In reply to comment #2) > P.S. Maybe I'm sending too many reports, sorry if that :) at least this is a dupe. you suffer from bad X11 performance on texture_prom_pixmap in the nvidia css driver (or pot. any conversion method) - have you ever checked your /var/log/Xorg.0.log (esp. have a look for "WW", "EE" and "dri") grep -E '(EE|WW|dri|DRI)' /var/log/Xorg.0.log - is X11 load high using the XRender backend as well? - sure you're actually using the nvidia css driver? glxinfo | grep -i version *** This bug has been marked as a duplicate of bug 234463 ***