Need help to diagnose slowdown problem

[Samuel Gilbert]

Hello everyone,

  Ever since I've started using KDE4 on 3 different systems, I'm having 
performance problems.  Here is what happens :

After working in a session for a while the Xorg process starts to take more 
and more CPU.  I will generally notice it when some actions such as scrolling 
in dolphin or typing in kmail are totally unresponsive.  The subjective effect 
is like running remote X applications through a slow 56.6Kbps modem 
connection.

I have found a 100% reproducible way to trigger the problem : All I have to do 
is to use digiKam's aspect crop tool on about 30 photographs.

When the problem occurs, the X server process will take around 10~15% CPU when 
there are absolutely no events going on.  Doing thing such as switching 
windows or scrolling in a existing window (Firefox, dolphin, ooffice, etc..) 
will cause the Xorg process to jump to 100% CPU usage.  Closing windows will 
help a little, but the only way to get Xorg to behave properly once again is 
to completely restart the session.

I have tried to disable composting both in KDE and directly in 
/etc/X11/Xorg.conf to no avail.  The problem occurs on 3 different systems 
that do not have the same versions of software components.  Here are the 
common factors :

Linux x86_64
Nvidia graphic cards (9400M, NVS 160M, 8300)
KDE >=4.4.2
Xorg >= 1.7.6

Two machines are laptops with Intel Core 2 CPUs and the other one is a desktop 
with an AMD CPU.  I also checked ~/.xsession-errors and /var/log/Xorg.0.log, 
but I didn't find anything that looked helpful to understand the issue I'm 
facing.

Any help and suggestions on how to diagnose what's going on will be greatly 
appreciated!

Cheers and happy holidays,
  Samuel