Mir is showing artifacts on intel graphics/T530 especially in dualscreen mode

[Benjamin Tegge]

I'm running saucy from an external harddrive. When multimonitor support landed a week ago, I noticed artifacts in dualscreen mode. I updated my installation and checked today, the artifacts are still there.

Systems tested:
Lenovo Thinkpad T530 with Ivy Bridge processor.
HP Probook 6460b with Sandy Bridge processor.

Artifacts seen:
- When moving the mouse, the a mouse trail can be seen. Additionally the cursor is randomly invisible and and the trail artifacts look interlaced and distorted. These artifacts are visible for more than 2 seconds.
- When opening a terminal, the terminal feels unresponsive showing inputs only after a few seconds. Executing apt-get update looks like the output is scrolling back and forth.

These artifacts are not visible with Mir disabled. With Mir in single monitor mode, I haven't noticed above artifacts but when moving windows fast there are few lines showing combing artifacts for a very short time and opening the power cog for the first time shows artifacts too, but the system is usable.

[Benjamin Tegge (livewirebt)]

I couldn't make screenshots showing the artifacts, so I tried making videos.
https://dl.dropboxusercontent.com/u/15877132/MVI_0254.MOV
https://dl.dropboxusercontent.com/u/15877132/MVI_0255.MOV

[Daniel van Vugt (vanvugt)]

Thanks. Both the issues you report are known already and being discussed here:
  Bug 1218735
  Bug 1216472