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Section on performance, just in case.

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svn path=/trunk/KDE/kdebase/workspace/; revision=758909
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Luboš Luňák 2008-01-09 14:41:27 +00:00
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NOTES_4_0
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@ -94,6 +94,36 @@ XXX link to 4.0 kwin video
XXX note the kwin_composite tag at youtube
= Performance =
Compositing internally works by redirecting window drawing to offscreen memory and composing
it on the screen in an additional drawing pass. This means that in general composited desktop
on average has worse performance that non-composited desktop (although in some cases it
may perform better, be that real improvement or just perceived one due to animations, better
synchronization or similar factors). For example, binding window pixmaps to OpenGL textures
(that is, preparing window contents for drawing) can be a relatively costly operation
with large windows, making things like animations in Plasma desktop window or page scrolling
in a maximized browser window jerky. Heavy system load can also cause the compositing manager
not repaint often enough, resulting in lagging or jerky screen redrawing.
KWin in KDE4.0 is also relatively new code and has not been extensively optimized yet,
therefore its performance may not be in some areas comparable with performance of other
compositing managers. In such cases performance should be improved with newer versions.
Note that current XRender implementations (in X/drivers) often perform rather poorly and
therefore the OpenGL mode usually should have much better performance. See below for notes
on XRender mode.
Tip: Performance/smoothness with nVidia cards: Smoothness of KWin rendering
can be improved by setting env.variable KWIN_NVIDIA_HACK to 1 (e.g. append
"export KWIN_NVIDIA_HACK=1" to your ~/.profile file). This sets __GL_YIELD=NOTHING
for KWin, letting KWin use more CPU time for OpenGL operations, however
at the expense of affecting performance of other applications. This is
therefore disabled by default. This setting may be removed in the future
if the negative impact becomes insignificant. See section "OPENGL YIELD BEHAVIOR"
in README.txt for nVidia cards.
= Troubleshooting =
As already said, compositing support in KWin is considered usable and reasonably stable,
@ -114,7 +144,7 @@ See file
XXX http://websvn.kde.org/*checkout*/trunk/KDE/kdebase/workspace/kwin/COMPOSITE_HOWTO
for some issues with various graphics cards.
See other sections below for further possible problems.
XXX See other sections below for further possible problems.
= XRender mode =
@ -145,17 +175,9 @@ to use source code of effects shipped with KWin (the Howto effect as the startin
XXX link to kwin sources?
and/or ask on the KWin mailing list XXX link.
Links to various KWin-related documents are available at XXX http://techbase.kde.org/Projects/KWin .
= Various =
- Performance/smoothness with nVidia cards: Smoothness of KWin rendering
can be improved by setting env.variable KWIN_NVIDIA_HACK to 1 (e.g. append
"export KWIN_NVIDIA_HACK=1" to your ~/.profile file). This sets __GL_YIELD=NOTHING
for KWin, letting KWin use more CPU time for OpenGL operations, however
at the expense of affecting performance of other applications. This is
therefore disabled by default. This setting may be removed in the future
if the negative impact becomes insignificant. See section "OPENGL YIELD BEHAVIOR"
in README.txt for nVidia cards.
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