bug#14051: Fwd: 24.3; Slow scrolling in term modes

bug#14051: Fwd: 24.3; Slow scrolling in term modes

[Bryan Bishop]

This bug report will be sent to the Bug-GNU-Emacs mailing list
and the GNU bug tracker at debbugs.gnu.org.  Please check that
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Please write in English if possible, as the Emacs maintainers
usually do not have translators for other languages.

Please describe exactly what actions triggered the bug, and
the precise symptoms of the bug.  If you can, give a recipe
starting from `emacs -Q':




The window scrolling performance ("multi-term" and plain old "term" in
this case) in emacs 24 is terrible after a few thousand lines of
scrollback, slowly getting worse and worse and after about 5000 lines of
scrollback takes about a 1/2 second to render the next chunk of text.

How I can replicate the problem:

emacs -Q
M-x term
find /

(The output of the find command whizzes by, and then starts to get jerky
and slow when scrollback history is > 2000 lines)

I've installed the stock emacs24 from linux mint/ubuntu packages
(24.1.1), and a custom
compiled version of 24.3.1 without any special tricks and a compiler
option of -O3 and the term mode behavior is all the same, and this
behavior even shows up with "emacs -Q".

It seems the same with multi-term, ansi-term, nterm, it doesn't matter.
This does work very fast in eshell and in terminal-emulator mode.
What is weird is ALL the terminal modes in Emacs 23 seem to work
great, but not Emacs 24.

Any ideas how I can make this mode faster?  My suspicion was around
font-lock-mode but I've turned that off with no effect.  The fact that
it is still slow without my init file using -Q and seems to be really
fast in Emacs 23 has me stumped.



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'.
For information about debugging Emacs, please read the file
/usr/local/share/emacs/24.3/etc/DEBUG.


In GNU Emacs 24.3.1 (x86_64-unknown-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2013-03-13 on badwolf
Windowing system distributor `The X.Org Foundation', version 11.0.11300000
System Description:    Linux Mint 14 Nadia

Configured using:
 `configure '--prefix=/usr/local' 'CFLAGS=-O3''

Important settings:
  value of $LC_CTYPE: en_US.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Buffer Menu

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

Recent input:
C-x 1 M-x t e r m <return> <return>
f i n d <return> C-c C-c C-c C-c C-c C-c e x i t <return>

Recent messages:
byte-code: Beginning of buffer [14 times]
Quit [2 times]
Mark set
Sending...
Already sent message via mail; resend? (y or n)  y
Mark set [2 times]
Sending via mail...
Sending...done
Mark set
Saved text from "The window scrolling performance ("multi"

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bug#14051: Fwd: 24.3; Slow scrolling in term modes

[Stefan Kangas]

Bryan Bishop <bryanjbishop@yahoo.com> writes:

> The window scrolling performance ("multi-term" and plain old "term" in
> this case) in emacs 24 is terrible after a few thousand lines of
> scrollback, slowly getting worse and worse and after about 5000 lines of
> scrollback takes about a 1/2 second to render the next chunk of text.
>
> How I can replicate the problem:
>
> emacs -Q
> M-x term
> find /
>
> (The output of the find command whizzes by, and then starts to get jerky
> and slow when scrollback history is > 2000 lines)
>
> I've installed the stock emacs24 from linux mint/ubuntu packages
> (24.1.1), and a custom
> compiled version of 24.3.1 without any special tricks and a compiler
> option of -O3 and the term mode behavior is all the same, and this
> behavior even shows up with "emacs -Q".
>
> It seems the same with multi-term, ansi-term, nterm, it doesn't matter.
> This does work very fast in eshell and in terminal-emulator mode.
> What is weird is ALL the terminal modes in Emacs 23 seem to work
> great, but not Emacs 24.
>
> Any ideas how I can make this mode faster?  My suspicion was around
> font-lock-mode but I've turned that off with no effect.  The fact that
> it is still slow without my init file using -Q and seems to be really
> fast in Emacs 23 has me stumped.

Yes.  Both term and ansi-term and significantly slower than eshell when
running "find /".

I had a suspicion that it was because of term-buffer-maximum-size, but
setting this to 0 made no difference.

(BTW, maybe the default term-buffer-maximum-size should be raised from
the default 2048?  For example to (* 4 2048).)

Best regards,
Stefan Kangas

bug#14051: Fwd: 24.3; Slow scrolling in term modes

[Eli Zaretskii]

> Date: Mon, 30 Sep 2019 18:19:25 +0200
> Cc: 14051@debbugs.gnu.org
> 
> Yes.  Both term and ansi-term and significantly slower than eshell when
> running "find /".

If you customize your shell prompt to include a newline (i.e produce
an empty line), does it help to produce faster scrolling?

bug#14051: Fwd: 24.3; Slow scrolling in term modes

[Phil Sainty]

If this bug is still about Emacs 24, does the following help?

  ;; Terminal buffer configuration.
  (add-hook 'term-mode-hook 'my-term-mode-hook)
  (defun my-term-mode-hook ()
    ;; https://debbugs.gnu.org/cgi/bugreport.cgi?bug=20611
    (setq bidi-paragraph-direction 'left-to-right))

You would only need to use this hook for Emacs 24.x -- this
particular issue was dealt with by default in Emacs 25+.


-Phil

bug#14051: Fwd: 24.3; Slow scrolling in term modes

[Lars Ingebrigtsen]

Bryan Bishop <bryanjbishop@yahoo.com> writes:

> How I can replicate the problem:
>
> emacs -Q
> M-x term
> find /
>
> (The output of the find command whizzes by, and then starts to get jerky
> and slow when scrollback history is > 2000 lines)

(I'm going through old bug reports that unfortunately weren't resolved
at the time.)

I tried reproducing this in Emacs 28, but I can't see any particular
slowdowns in this situation.  Are you still seeing this issue in recent
Emacs versions?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#14051: Fwd: 24.3; Slow scrolling in term modes

[Lars Ingebrigtsen]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> I tried reproducing this in Emacs 28, but I can't see any particular
> slowdowns in this situation.  Are you still seeing this issue in recent
> Emacs versions?

More information was requested, but no response was given within a
month, so I'm closing this bug report.  If the problem still exists,
please respond to this email and we'll reopen the bug report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no