bug#17404: Scrolling is painfully slow

[Eli Zaretskii]

> Date: Mon, 05 May 2014 02:59:28 -0400
> From: Richard Stallman <rms@gnu.org>
> 
>     [19295] 2014-05-01 17:15:29.522 INFO: Updated to revision 117039 of 
> branch bzr+ssh://rms@bzr.savannah.gnu.org/emacs/trunk
> 
> If you visit the file below in Rmail and type C-s GNU Emacs,
> then C-n takes around 15 seconds.

It takes less than 0.5 sec here.  My machine is faster than yours, but
I doubt that it's 30 times faster.

That file has 2 very long lines, one 42K characters long, the other
80K characters long, and Emacs display engine is known to be very slow
with such long lines.

If you have older Emacs 24.x installations somewhere, can you try the
same with those?  I don't think something's changed significantly in
this area since Emacs 24.1, where bidirectional display slowed such
long lines some more.