(In reply to David Francis from comment #18)
> My hypothesis is that has something to do with the mouse polling rate.  

What is that hypothesis based on?

The kernel is supposed to be able to process any number of
DRM_IOCTL_MODE_CURSOR(2) ioctls in parallel with a DRM_IOCTL_MODE_PAGE_FLIP
ioctl, without them interfering with each other. Most likely there's an issue
in the DC code interfering this. See the patch I referenced in comment 17 for
an example of what might need to be done to solve this.