Comment 30 for bug 1690719

This lag has been present as far as I remember using GNOME 3 on my laptop. In fact, the move to Wayland exposes it clearly because it makes the mouse cursor freeze. I wrote a shell extension to expose the lag https://extensions.gnome.org/extension/929/buttercheck/ (not yet updated for 3.16) and it happens even on X11.

Another way to show it:
- Alt + F2, "r" and hit return to have a fresh shell
- Open a video and play it
- Hit Super + A
- The shell will stall for at least one full second. That's on a Sandy Bridge laptop with a SSD... not exactly a weak computer.

My best guess here is that the shell uses Meta.LaterType.BEFORE_REDRAW all over the place: https://github.com/GNOME/gnome-shell/search?utf8=%E2%9C%93&q=BEFORE_REDRAW
This causes Clutter to wait for the completion of these events before starting to draw a frame. But, these events generally take a few msc to a few seconds to complete, effectively stalling the entire shell.

After writing this comment I'm gonna measure these stalls and post them here.