bug#44464: 28.0.50; slow shell output

[Basil L. Contovounesios]

Eli Zaretskii <eliz@gnu.org> writes:

>> Cc: 44464@debbugs.gnu.org, Eli Zaretskii <eliz@gnu.org>
>> From: Phil Sainty <psainty@orcon.net.nz>
>> Date: Fri, 6 Nov 2020 02:54:17 +1300
>> 
>> I can reproduce the issue (in 27.1), and it seems to me that it's
>> all about that one paragraph of right-to-left text.
>> 
>> If I disable `bidi-display-reordering', I see no slow-downs.
>
> I don't see any particularly bad slowdown at all, but maybe I didn't
> make all the steps (I don't have 'curl').  Do you see the same
> slowdown if you fetch the URL with, say, WGET, and then visit it in
> Emacs?  If not, how to reproduce this without 'curl'?

0. emacs -Q
1. M-x shell RET
2. C-x 1
3. wget -O- http://dbpedia.org/resource/Earth
4. RET

The printing to *shell* happens at a speed that I'm accustomed to in
Emacs shell emulators, but there's a noticeable pause for a fraction of
a second at a couple of lines, one of which contains Arabic script.

While printing, the last line is also highlighted in blue, i.e. with the
comint-highlight-prompt face.  You can also see this with e.g.

  $ while :; do printf hi; sleep 1; done

-- 
Basil

In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo version 
1.16.0, Xaw3d scroll bars)
 of 2020-11-05 built on thunk
Repository revision: 771046f5d888c703c875d8629fdf227429a36d3d
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Debian GNU/Linux bullseye/sid

Configured using:
 'configure 'CC=ccache gcc' 'CFLAGS=-O2 -march=native' --config-cache
 --prefix=/home/blc/.local --with-x-toolkit=lucid
 --with-file-notification=yes --with-x'

Configured features:
XAW3D XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND GPM DBUS GSETTINGS GLIB
NOTIFY INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT
LIBOTF ZLIB TOOLKIT_SCROLL_BARS LUCID X11 XDBE XIM MODULES THREADS
LIBSYSTEMD JSON PDUMPER LCMS2

Important settings:
  value of $LANG: en_IE.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix