1. Use r600g as of today ("eselect mesa r600 set gallium" on Gentoo)
2. Enable desktop effects in kwin
3. kwin now uses 100% CPU doing.. who knows.

I've tried disabling every effect in kwin, doesn't matter. Tried changing other settings also, makes no difference. kwin works fine with r600c.

I started kwin, waited a while, it keeps on using 100% CPU forever so how long should not matter, and ran gdb kdm $pid. bt gave this: 

------------------------------------------
(gdb) bt
#0  0x00007fe94bb7101b in memcpy () from /lib/libc.so.6
#1  0x00007fe931000379 in util_copy_rect () from /usr/lib64/dri/r600_dri.so
#2  0x00007fe9310020c5 in util_resource_copy_region ()
   from /usr/lib64/dri/r600_dri.so
#3  0x00007fe930f75c30 in st_texture_image_copy ()
   from /usr/lib64/dri/r600_dri.so
#4  0x00007fe930fac50d in st_finalize_texture ()
   from /usr/lib64/dri/r600_dri.so
#5  0x00007fe930fa1698 in finalize_textures () from /usr/lib64/dri/r600_dri.so
#6  0x00007fe930f9e306 in st_validate_state () from /usr/lib64/dri/r600_dri.so
#7  0x00007fe930f72885 in st_draw_vbo () from /usr/lib64/dri/r600_dri.so
#8  0x00007fe930f97b64 in vbo_exec_vtx_flush () from /usr/lib64/dri/r600_dri.so
#9  0x00007fe930f933c5 in vbo_exec_FlushVertices_internal ()
   from /usr/lib64/dri/r600_dri.so
#10 0x00007fe930f95212 in vbo_exec_FlushVertices ()
   from /usr/lib64/dri/r600_dri.so
#11 0x00007fe930e856e6 in _mesa_PopAttrib () from /usr/lib64/dri/r600_dri.so
#12 0x00007fe94a4a5ca0 in KWin::PaintClipper::Iterator::~Iterator() ()
   from /usr/lib/libkwineffects.so.1
#13 0x00007fe94a4b1a68 in KWin::renderGLGeometry(QRegion const&, int, float cons
t*, float const*, float const*, int, int) () from /usr/lib/libkwineffects.so.1
#14 0x00007fe94bf0de18 in KWin::SceneOpenGL::Window::renderQuads(int, QRegion co
nst&, KWin::WindowQuadList const&) () from /usr/lib/libkdeinit4_kwin.so
#15 0x00007fe94bf121b4 in KWin::SceneOpenGL::Window::performPaint(int, QRegion,
KWin::WindowPaintData) () from /usr/lib/libkdeinit4_kwin.so
#16 0x00007fe94bf0303e in KWin::Scene::finalDrawWindow(KWin::EffectWindowImpl*,
int, QRegion, KWin::WindowPaintData&) () from /usr/lib/libkdeinit4_kwin.so
#17 0x00007fe94bf1b855 in KWin::EffectsHandlerImpl::drawWindow(KWin::EffectWindo
w*, int, QRegion, KWin::WindowPaintData&) () from /usr/lib/libkdeinit4_kwin.so
#18 0x00007fe94bf01f2b in KWin::Scene::finalPaintWindow(KWin::EffectWindowImpl*, int, QRegion, KWin::WindowPaintData&) () from /usr/lib/libkdeinit4_kwin.so
#19 0x00007fe94bf1b955 in KWin::EffectsHandlerImpl::paintWindow(KWin::EffectWindow*, int, QRegion, KWin::WindowPaintData&) () from /usr/lib/libkdeinit4_kwin.so
#20 0x00007fe94bf03a4c in KWin::Scene::paintWindow(KWin::Scene::Window*, int, QRegion, KWin::WindowQuadList) () from /usr/lib/libkdeinit4_kwin.so
#21 0x00007fe94bf04f67 in KWin::Scene::paintSimpleScreen(int, QRegion) ()
   from /usr/lib/libkdeinit4_kwin.so
#22 0x00007fe94bf01f77 in KWin::Scene::finalPaintScreen(int, QRegion, KWin::ScreenPaintData&) () from /usr/lib/libkdeinit4_kwin.so
#23 0x00007fe94bf1ba52 in KWin::EffectsHandlerImpl::paintScreen(int, QRegion, KWin::ScreenPaintData&) () from /usr/lib/libkdeinit4_kwin.so
#24 0x00007fe94bf03c75 in KWin::Scene::paintScreen(int*, QRegion*) ()
   from /usr/lib/libkdeinit4_kwin.so
#25 0x00007fe94bf13d9f in KWin::SceneOpenGL::paint(QRegion, QList<KWin::Toplevel*>) () from /usr/lib/libkdeinit4_kwin.so
#26 0x00007fe94befe87c in KWin::Workspace::performCompositing() ()
   from /usr/lib/libkdeinit4_kwin.so
#27 0x00007fe94be827c2 in KWin::Workspace::qt_metacall(QMetaObject::Call, int, void**) () from /usr/lib/libkdeinit4_kwin.so
#28 0x00007fe94776fda6 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib64/qt4/libQtCore.so.4
#29 0x00007fe94776c656 in QObject::event(QEvent*) ()
   from /usr/lib64/qt4/libQtCore.so.4
#30 0x00007fe94838cecc in QApplicationPrivate::notify_helper(QObject*, QEvent*)
    () from /usr/lib64/qt4/libQtGui.so.4
#31 0x00007fe9483934cb in QApplication::notify(QObject*, QEvent*) ()
   from /usr/lib64/qt4/libQtGui.so.4
#32 0x00007fe94b6cc0e8 in KApplication::notify(QObject*, QEvent*) ()
   from /usr/lib/libkdeui.so.5
#33 0x00007fe94775cb0b in QCoreApplication::notifyInternal(QObject*, QEvent*)
    () from /usr/lib64/qt4/libQtCore.so.4
#34 0x00007fe94778957a in ?? () from /usr/lib64/qt4/libQtCore.so.4
#35 0x00007fe94778978b in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop:---Type <return> to continue, or q <return> to quit---
:ProcessEventsFlag>) () from /usr/lib64/qt4/libQtCore.so.4
#36 0x00007fe94843cc15 in ?? () from /usr/lib64/qt4/libQtGui.so.4
#37 0x00007fe94775b432 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/qt4/libQtCore.so.4
#38 0x00007fe94775b7fd in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/qt4/libQtCore.so.4
#39 0x00007fe94776043b in QCoreApplication::exec() ()
   from /usr/lib64/qt4/libQtCore.so.4
#40 0x00007fe94be9d43b in kdemain () from /usr/lib/libkdeinit4_kwin.so
#41 0x00007fe94bb0ebbd in __libc_start_main () from /lib/libc.so.6
#42 0x00000000004006e9 in _start ()
(gdb) quit
A debugging session is active.

        Inferior 1 [process 379] will be detached.

Quit anyway? (y or n) y
Detaching from program: /usr/bin/kwin, process 379
------------------------------------------

I have no idea if the bt help anything at all. Please let me know if I can somehow provide any usefull information and how to get it.

Also, I've whined like a spoiled child about this here: http://www.phoronix.com/forums/showthread.php?t=26196