I found https://wiki.ubuntu.com/X/Troubleshooting/HighCPU
$ glxinfo |grep render direct rendering: Yes OpenGL renderer string: Mesa DRI Intel(R) Sandybridge Mobile GL_NV_conditional_render, GL_AMD_draw_buffers_blend, killing applications one-by-one is not really an option since I cannot reproduce the condition reliably. /var/log/Xorg.0.log.old says: [ 14125.830] (EE) intel(0): Detected a hung GPU, disabling acceleration. [ 14125.830] (EE) intel(0): When reporting this, please include i915_error_state from debugfs and the full dmesg. /var/log/kern.log: May 20 13:11:53 t520sds kernel: [14108.121616] [drm:i915_hangcheck_hung] *ERROR* Hangcheck timer elapsed... GPU hung May 20 13:11:53 t520sds kernel: [14108.121620] [drm] capturing error event; look for more information in /debug/dri/0/i915_error_state May 20 13:11:53 t520sds kernel: [14108.137584] [drm:__gen6_gt_force_wake_get] *ERROR* Timed out waiting for forcewake old ack to clear. ** Summary changed: - Xorg is pegged constantly redrawing the panel + GPU lockup: Xorg is pegged - constantly redrawing the panel -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1182156 Title: GPU lockup: Xorg is pegged - constantly redrawing the panel To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/1182156/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs