bug#28695: 26.0.60; Rendering lag spikes caused by double-buffering on Linux

[Bryan Gilbert <bryan@bryan.sh>]

> Eli Zaretskii <eliz@gnu.org> writes:
>
> Can you try lowering the screen resolution and using fullscreen Emacs
> frames under that lower resolution?
>
> Thanks.

I just flipped the resolution down to 1080p and it became barely noticeable.
Here's is quick screen capture:

  http://drop.bryan.sh/UImFf4Rnzf.mp4

You can still slightly see it doing something weird with glxgears. However,
without that visual indication on the screen it feels almost on par with double
buffering being disabled.

I'll also mention that apart from this being reliably reproduced while using
counsel-rg, I've been hard pressed to notice it in other places. For a while,
I even thought that this may have been a bug with Ivy until I found the commit
that introduced the slowdown. This coupled with the possibility that it's only
visible at higher resolutions may be why many people aren't experiencing issues.