drm-next-kmod regression

Hi,
the last drm-next-kmod worked fine on my Lenovo T420 with i5-2520M and a 
HD Graphics 3000. After the update to the actual version (4.11) from 
ports, I'm seeing regression in form of a very slow xfce4-desktop. The 
slowness starts after some short time. Slow means for example that I can 
type faster than the terminal prints the chars or when i move windows 
they lag extremely behind the mouse's motion.

One entry in Xorg.0.log caught my attention:
[   128.266] (EE) intel(0): Failed to submit rendering commands (Bad 
address), disabling acceleration.

Disabling the xfce4-compositor improves the situation significantly, but 
not entirely.

Switching back to the systems i915 driver resolves the issue.

Any ideas?