bug#16830: [Bug] 24.3.50; massive slow down in forward-line

[Eli Zaretskii]

> Date: Sat, 22 Feb 2014 12:08:58 +0100
> From: "Stefan-W. Hahn" <stefan.hahn@s-hahn.de>
> Cc: 16830@debbugs.gnu.org
> 
> > OK, I can confirm the slow-down.  The profile points to forward-line,
> > so I disabled cache-long-scans, and -- lo and behold -- the slowdown
> > went away.  So this should be the workaround for the time being.
> 
> Sounds good. Is it right that I can set this variable globally only by
> installing a function setting it in find-file-hook?

Doesn't sound like a good idea to me: that would disable the caching
for much more than this Org file, or even just Org files, right?  I
would suggest to selectively disable caching only for those files that
are actually affected in perceptible way, because the caching in
general does speed up things.

> I tested it that way with my original file.
> (elp-instrument-package org; elp-result for org-ctrl-c-ctrl-c)
> 
> emacs 24.3.50.1    2.083 sec (cache-long-scans nil, set by file-find-hook)
> emacs 24.3.1       0.758 sec (cache-long-line-scan nil; as it was)
> 
> So it is better, but not so good as in the old emacs.

I see no difference in the code that could justify this, and on my
system "C-c C-c" in both versions completes in the same time after
disabling the caching, certainly much faster than 2 sec.  So I don't
see how such a 2.5 factor could be explained, except perhaps by some
additional local customizations on your system (I tested in "emacs -Q").