Subject: bug#8333: 24.0.50; Performace regression from r100619 try_scrolling change

From: Chong Yidong <[email-masked]>
Date: Wed, 23 Mar 2011 17:39:37 -0400

2010-06-19  Eli Zaretskii  <[email-masked]>

  * xdisp.c (try_scrolling): Compute the limit for searching point
  in forward scroll from scroll_max, instead of an arbitrary limit
  of 10 screen lines.  See
  http://lists.gnu.org/archive/html/emacs-devel/2010-06/msg00766.html
  and
  http://lists.gnu.org/archive/html/emacs-devel/2010-06/msg00773.html
  for details.

This change (on trunk) causes a big slowdown in navigating large
buffers.  To reproduce, make a .emacs with just the following line:

(setq scroll-conservatively 1000)

Then:

emacs /path/to/xdisp.c
M-g M-g 20000 RET

Emacs takes about a second to move point to the specified line.  If the
above change is reverted, moving is instantaneous.  The slowdown is much
more apparent if Emacs is compiled without optimizations.

In GNU Emacs 24.0.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.20.1)
 of 2011-03-23 on furball
Windowing system distributor `The X.Org Foundation', version 11.0.10706000
configured using `configure  'CC=gcc' 'CFLAGS=-g''