bug#44464: 28.0.50; slow shell output

["Andreas Röhler" <andreas.roehler@easy-emacs.de>]

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When running

curl -L -H "Accept: text/html" http://dbpedia.org/resource/Earth

output stops at several times.
It fontifies parts of the output - fontification is gone when finished. 
See attachments for freezes during output

No delay in system bash BTW.

In GNU Emacs 28.0.50 (build 1, i686-pc-linux-gnu, GTK+ Version 3.14.5, 
cairo version 1.14.0)
  of 2020-06-10
Repository revision: ee8b2742d7f6d03daea37f1bac48c2746f7ca789
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.11604000
System Description: Debian GNU/Linux 8 (jessie)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Mark set [4 times]
Quit
Mark set
5 0

Configured using:
  'configure --with-modules --with-mailutils'

Configured features:
XPM JPEG TIFF GIF PNG CAIRO SOUND DBUS GSETTINGS GLIB NOTIFY INOTIFY ACL
GNUTLS LIBXML2 FREETYPE LIBOTF ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE
XIM MODULES THREADS PDUMPER GMP

Important settings:
   value of $LANG: de_DE.UTF-8
   locale-coding-system: utf-8-unix

Major mode: Shell

Minor modes in effect:
   shell-dirtrack-mode: t
   tooltip-mode: t
   global-eldoc-mode: t
   electric-indent-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
   line-number-mode: t
   transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search seq
byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils time-date subr-x
cl-loaddefs cl-lib shell pcomplete comint ansi-color ring tooltip eldoc
electric uniquify ediff-hook vc-hooks lisp-float-type mwheel term/x-win
x-win term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame minibuffer cl-generic cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms
cp51932 hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese composite charscript charprop case-table epa-hook
jka-cmpr-hook help simple abbrev obarray cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote threads dbusbind inotify dynamic-setting system-font-setting
font-render-setting cairo move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 8 173153 8669)
  (symbols 24 30041 1)
  (strings 16 65618 1981)
  (string-bytes 1 1087478)
  (vectors 8 13865)
  (vector-slots 4 381518 22024)
  (floats 8 25 46)
  (intervals 28 2390 2)
  (buffers 564 11)
  (heap 1024 15133 888))


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