Alongside the backtraces you posted this very much seems to be an issue in the fglrx driver.
Esp. crashing X11 is a rather really bad sign - i would check whether there's a newer version, if not whether you can downgrade and also report this to AMD.

For KWin you can try
KWIN_DIRECT_GL= LIBGL_ALWAYS_INDIRECT=1 kwin --replace &
^^^ that blank is intentional

but this will at best release some stress from the driver, not fix it.
(Plus, you'll loose OpenGL 2 support, esp. glsl)

luebking wrote:Alongside the backtraces you posted this very much seems to be an issue in the fglrx driver.
Esp. crashing X11 is a rather really bad sign - i would check whether there's a newer version, if not whether you can downgrade and also report this to AMD.

For KWin you can try
KWIN_DIRECT_GL= LIBGL_ALWAYS_INDIRECT=1 kwin --replace &
^^^ that blank is intentional

but this will at best release some stress from the driver, not fix it.
(Plus, you'll loose OpenGL 2 support, esp. glsl)

I put these variables in a script inside $KDEHOME/env/. I also removed all the activities because "lagginesh" get occasionally triggered and do persist after switching between some of these, whilst the primary activity seems to be immune from lagginesh. Don't know if that is meaningful, it does happen, though. Let's see how it'll behave.

One week later:

Window resizing started to suffer from lags only on desktop 1 (the virtual desktop I use the most), whilst on the other three desktops (even with the exactly same windows and same window positions of the first one) continues to be as fast as it was when I first logged in. Could it also be a problem related to the fglrx driver?

frasty wrote:Could it also be a problem related to the fglrx driver?

Quite likely. The driver is unfortunately known to create problems in all areas. I have been seriously considering over the last weeks to completely blacklist the driver in the next release if the situation doesn't improve.

frasty wrote:Window resizing started to suffer from lags only on desktop 1

FYI: it is *highly* unlikely that this is related to the particular VD id - it will be the amount of windows or the contents of a particular window (could even be the desktop) that cause some slowdown or block a bottleneck in the system, leading to this situation.

luebking wrote:

frasty wrote:Window resizing started to suffer from lags only on desktop 1

FYI: it is *highly* unlikely that this is related to the particular VD id - it will be the amount of windows or the contents of a particular window (could even be the desktop) that cause some slowdown or block a bottleneck in the system, leading to this situation.

I think I'll try from within a KDE4.10 live distro (if any) and I'll let you know if I'll still have these perfomance problems.