Comment 48 for bug 1714178

Here is the first version of the patchset: https://cgit.freedesktop.org/~mperes/xserver/log/?h=3x4k

This has 0 performance cost unless we need to enable the feature because we exceed the driver's limits (what happens on Intel HW for 3x4k). In this case, we start using a buffer per-crtc and blit to it whenever there are damages on the screen.

This is pretty much the optimal behaviour performance-wise in a composited environment (unless the kernel lifts the limits I was talking about in the last comment). However, in non-composited environments, we can further improve this by blitting the damages no more than once per frame (hoping for some of the damages to overlap). I will get to that next week.

Also happening next week is more testing, and verifying that this also works without glamor and with the other options of modesetting.