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|Before making any changes to your system, please read everything carefully and try to understand what you are doing. If you're modifying any files on your system, keep copies of the unmodified version and be sure you can revert to those old version - even if your Xserver is not starting any longer.|
|Some of the changes mentioned below are said to increase the temperature of your GPU. In any case, monitor your graphic card to make sure it isn't getting too hot!|
Several popular graphics cards out there - especially NVIDIA ones - exhibit performance problems with KDE4. These performance hits mostly concern Plasma - the KDE4 desktop - and KWin - the KDE window-manager. Generally speaking this isn't due to KDE4 being unoptimized but a problem with the cards' graphics drivers. This page encompasses certain problems that might arise and how to get rid of them.
For both of the big graphics chip manufacturers there's 2 seperate graphics drivers each:
Update: Nvidia has recently issued a new beta driver which is supposed to address most of the performance problems seen with KDE4. It can be downloaded in  64bit and  32bit. You need to add some options to your xorg.conf and enable certain feature at runtime, see  this post on the NvNews forums for details. Note: Only install beta drivers if you know what you are doing.
|TODO: section about radeonhd and fglrx driver - I don't own an ATI card Lemma|
It's usually advisable to stay up-to-date as improvements are being made in the drivers. Thus a first step in improving your KDE4 experience should be checking your current driver and updating if it's outdated. Please refer to your distribution's documentation on how to do that.
While it might further increase performance, I do NOT recommend installing beta quality drivers because your system's stability will most likely suffer.
Attributes set using the nvidia-settings utility aren't permanently saved. Thus you have to set them every time you restart your Xserver. This can be done conveniently by adding the lines to set the features to your ~/.xinitrc.
KDE4's systemsettings allows you to tweak some kwin settings as well. You can find the settings in Desktop -> Desktop Effects -> Advanced Options. Depending on your card either OpenGL or XRender might work better. For OpenGL changing the OpenGL mode might change performance as well. Please bear in mind that changing some of the tweaks mentioned below might force you to change your settings.
(note from a user)* Not selecting "Use Vsync" helped a lot in a gforce 6800 (and also on a GeForce 8400M GT).
If for some reason your Xserver hangs after hitting the Apply button on the dialog and your settings get reverted because you can't confirm your changes in time, try again. Usually it will be faster on one of the subsequent tries. If it doesn't you can still change your settings in ~/.kde4/share/config/kwinrc.
This section summarizes several symptoms you might encounter and tries to explain possible causes.
$ XLIB_SKIP_ARGB_VISUALS=1 konsoleon the command-line and try to resize the new konsole window (setting the environment variable XLIB_SKIP_ARGB_VISUALS turns off ARGB visuals). If it resizes without problems, then this is certainly one of the problems you're facing.
Note: I have found that this fixes Dolphin's preview delay too for me. Please confirm. --dpalacio 17:33, 27 July 2008 (CEST)
Section "Device" ... Option "BackingStore" "true" ... EndSection "Device"This works for some (eg. konsole) but unfortunately not all windows.
$ nvidia-settings -a InitialPixmapPlacement=2This works for some (but unfortunately not all) NVIDIA cards.
Section "Device" ... Option "AccelMethod" "EXA" # optional, may improve performance but introduce visible artifacts # Option "MigrationHeuristic" "greedy" ... EndSection "Device"
Performance will be somewhat better on older X servers (<=1.4.2) and significantly better on the latest prerelease X servers (>=188.8.131.521) with this option.
$ nvidia-settings -a InitialPixmapPlacement=2 -a GlyphCache=1This works for some (but unfortunately not all) NVIDIA cards. Some cards reportedly work better using InitialPixmapPlacement=1 (or maybe even 3)
The Open Source radeon driver uses the older XAA hardware acceleration method. To work around this issue, you have to change the 2D acceleration method from XAA (X Acceleration Architecture) to the newer EXA. As this involves editing your xorg.conf file, bear in mind that such a modification may damage your system. Do it at your own risk.
To make the switch, edit your xorg.conf file (make a backup just in case) and locate the Device section for your graphics card. Add the line
Option "AccelMethod" "EXA"
before the "EndSection" line. If there is already a line with AccelMethod, change it from XAA to EXA. Save the file and restart the X server. Notice that EXA is still marked as unstable, and that some other applications such as some KDE3 programs may render incorrectly.
When using EXA it is strongly recommended to use a recent X server, at least 1.4.2 or even better the 1.5 release candidates.