GNU bug report logs - #9589
23.1; Excessive CPU consumption for VERY long lines

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From: "Ludwig, Mark" <ludwig.mark@HIDDEN>
To: "bug-gnu-emacs@HIDDEN" <bug-gnu-emacs@HIDDEN>
Subject: 23.1; Excessive CPU consumption for VERY long lines
Thread-Topic: 23.1; Excessive CPU consumption for VERY long lines
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Please write in English if possible, because the Emacs maintainers
usually do not have translators to read other languages for them.

Your bug report will be posted to the bug-gnu-emacs@HIDDEN mailing list,
and to the gnu.emacs.bug news group.

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

The information below (about the instance of Emacs in which I started this =
bug report) is irrelevant, because the problem was not exercised in this in=
stance of Emacs, but I have left it, lest I be accused of not supplying the=
 standard text.

The problem context is a text file with one or more extremely long lines.  =
For example, you may use C-u 8 0 0 0 0 0 . (to get 800,000 "." characters).=
  Do this in the middle of an otherwise normal text file that fills several=
 screens, so that starting at beginning of the buffer you may issue C-v at =
least once before the long line becomes visible, and similarly have suffici=
ent shorter lines at the end of the buffer so that you may issue M-v at lea=
st once before the long line becomes visible.  The problem is that some com=
mands work very slowly when this long line is visible (in the case of C-v, =
M-v and C-l) while others are quick.  Once point is positioned in the long =
line, I found that the quick commands include C-a, M-b, M-<, and M->.  Slow=
 commands include C-e, M-f, C-p, and C-n.  I did not try to go through all =
of the movement commands to sniff out which are quick and which are slow.  =
On my machine, quick is instantaneous, while slow takes up to 7 seconds to =
respond.  The slowness seems to vary with the column of point (larger colum=
n number reported from C-x =3D).  Starting at the beginning of the long lin=
e, several C-v commands are quick, but they slow down as point moves furthe=
r into the long line.  The slowest position is the end of the line, where C=
-v and M-v take the most time.

I did not attempt to measure the performance with longer or shorter lines, =
but I imagine the slowness (for the slow commands) is linear with the lengt=
h of the line.  I leave that experimentation to you.

Thanks.

If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
    `bt full' and `xbacktrace'.
If you would like to further debug the crash, please read the file
c:/Apps/emacs-23.1/etc/DEBUG for instructions.


In GNU Emacs 23.1.1 (i386-mingw-nt6.1.7600)
 of 2009-07-29 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 6.1.7600
configured using `configure --with-gcc (4.4)'

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: ENU
  value of $XMODIFIERS: nil
  locale-coding-system: cp1252
  default-enable-multibyte-characters: t

Major mode: Text

Minor modes in effect:
  display-time-mode: t
  tooltip-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p=20
C-p C-l C-n C-n C-n C-n C-n C-p C-p C-p C-p C-p C-p=20
C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-SPC C-n=20
C-n C-n C-n C-w C-x C-s C-z <switch-frame> C-v <switch-frame>=20
C-p C-p C-p C-p C-p C-l C-n C-n C-SPC C-p C-p C-p C-p=20
C-p C-p C-p C-p C-p C-p C-w C-x C-s C-SPC C-p C-p C-p=20
C-p C-p C-p C-p C-w C-l C-SPC C-p C-p C-p C-p C-p C-p=20
C-p C-p C-p C-p C-p C-p C-p C-p C-w C-l C-x C-s C-p=20
C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p=20
C-p C-p C-SPC C-n C-n C-w C-l C-p C-p C-p C-p C-p C-SPC=20
C-n C-n C-n C-w C-k C-k C-k C-k C-k C-k C-p C-p C-p=20
C-p C-p C-l C-x C-s C-p C-p C-p C-p C-p C-p C-p C-p=20
C-p C-p C-p C-p C-p C-p C-p C-p C-k C-k C-k C-k C-k=20
C-k C-x C-s C-x C-o C-x C-s M-r M-v C-p C-p C-p C-p=20
C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p=20
C-p C-p C-p C-p C-p C-p C-p C-SPC C-n C-n C-n C-n C-n=20
C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n=20
C-n C-n C-n C-n C-n C-w C-x C-o C-l C-SPC C-p C-p C-p=20
C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-w=20
C-l C-x C-s C-l C-p C-p C-p C-p C-p C-p C-p C-p C-p=20
C-p C-p C-l M-v M-v M-v M-r C-p C-p C-p C-p C-p C-p=20
C-p C-p C-p C-p C-l C-p C-l C-p C-p C-p C-p C-p C-p=20
C-p C-p C-p C-p C-p C-l <help-echo> <help-echo> <help-echo>=20
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo>=20
<menu-bar> <help-menu> <send-emacs-bug-report>

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