Sync OpenBSD patchset 1072:

Add a simple form of output rate limiting by counting the number of
certain C0 sequences (linefeeds, backspaces, carriage returns) and if it
exceeds a threshold (current default 50/millisecond), start to redraw
the pane every 100 milliseconds instead of making each change as it
comes. Two configuration options - c0-change-trigger and
c0-change-interval.

This makes tmux much more responsive under very fast output (for example
yes(1) or accidentally cat'ing a large file) but may not be perfect on
all terminals and connections - feedback very welcome, particularly
where this change has a negative rather than positive effect (making it
off by default is a possibility).

After much experimentation based originally on a request Robin Lee
Powell (which ended with a completely different solution), this idea
from discussion with Ailin Nemui.

tmux.1

@@ -2467,6 +2467,24 @@ It may be switched off globally with:
 set-window-option -g automatic-rename off
 .Ed
 .Pp
+.It Ic c0-change-interval Ar interval
+.It Ic c0-change-trigger Ar trigger
+These two options configure a simple form of rate limiting for a pane.
+If
+.Nm
+sees more than
+.Ar trigger
+C0 sequences that modify the screen (for example, carriage returns, linefeeds
+or backspaces) in one millisecond, it will stop updating the pane immediately and
+instead redraw it entirely every
+.Ar interval
+milliseconds.
+This helps to prevent fast output (such as
+.Xr yes 1
+overwhelming the terminal).
+The default is a trigger of 50 and an interval of 100.
+A trigger of zero disables the rate limiting.
+.Pp
 .It Ic clock-mode-colour Ar colour
 Set clock colour.
 .Pp