I now tried Jesse Barnes' suggestion to add Option "ExaNoComposite" "true" to xorg.conf (I also added INTEL_BATCH="1" to /etc/environment).
When I rebooted performance seemed to be as good as it was with Intrepid. No more sluggishness. I opened many windows, alt tabbed between them and minimized in quick succession. All of it with reflection effect on but nothing happened. I started playing with other effects, turning them on and off and it froze after ten minutes while I was turning off some effect. I could not ssh from another computer. I was on a wifi link, that must have been the cause since it didn't hang. I was able to reboot doing alt sysrq R S E I U B.
Comment 214 belongs to me, sorry.
I now tried Jesse Barnes' suggestion to add Option "ExaNoComposite" "true" to xorg.conf (I also added INTEL_BATCH="1" to /etc/environment).
When I rebooted performance seemed to be as good as it was with Intrepid. No more sluggishness. I opened many windows, alt tabbed between them and minimized in quick succession. All of it with reflection effect on but nothing happened. I started playing with other effects, turning them on and off and it froze after ten minutes while I was turning off some effect. I could not ssh from another computer. I was on a wifi link, that must have been the cause since it didn't hang. I was able to reboot doing alt sysrq R S E I U B.