Comment 141 for bug 1690719

@Daniel
I'm testing these branches of yours on mutter:
https://i.imgur.com/gCDvaC8.png
and these (also from Marco) on gnome-shell:
https://i.imgur.com/A90c8y6.png

On the desktop (old gaming radeon card/wayland) the problem is almost solved, meaning that at least the cursor is not stopping for half a second when passing over a menubar with popovers opened.
On the intel laptop (z3735f/wayland) mouse still heavily lagging on menubars/shell popovers/most of gtk widgets and freezing for a good second and half when opening overview (the entire environment freeze when opening overview).
Unfortunately the 30/50% decrease in lag I was hoping for wasn't indipendent on platform's power.
Anyway, to not induce you or others to think that simply the system isn't powerful enough to sustain graphics acceleration, I'm again reinstating that on other wms (weston/kwin/compiz) the system is very smooth:
https://www.youtube.com/watch?v=-xSgzaoHO9Q

Great work! Let me know if I can help somehow.

Oscar