bug#32656: 27.0.50; Slow scrolling in Packages mode

[Sujith Manoharan]

Reverse scrolling in *Packages* is very slow. When the list
of packages is refreshed and shown after doing M-x list-packages,
jump to the end and then scroll backwards to see this
behavior. The issue is also seen with 'emacs -Q'.

I have this in my .emacs :
(add-to-list 'package-archives '("melpa" . 
"http://melpa.milkbox.net/packages/";))

This is the result of using the profiler:

- command-execute                                                2620  97%
 - call-interactively                                            2613  97%
  - funcall-interactively                                        2512  93%
     scroll-down-command                                         2438  90%
   - execute-extended-command                                      57   2%
    - sit-for                                                      47   1%
       redisplay                                                   40   1%
    - command-execute                                               7   0%
     - call-interactively                                           7   0%
      - funcall-interactively                                       7   0%
       - profiler-report                                            7   0%
        - profiler-report-cpu                                       7   0%
           profiler-cpu-profile                                     7   0%
     end-of-buffer                                                 17   0%
  - byte-code                                                     101   3%
   - read-extended-command                                        101   3%
    - completing-read                                             101   3%
     - completing-read-default                                    101   3%
        read-from-minibuffer                                       61   2%
- ...                                                              61   2%
   Automatic GC                                                    34   1%
 - minibuffer-complete                                             27   1%
  - completion-in-region                                           27   1%
   - completion--in-region                                         27   1%
    - #<compiled 0x1ddbb05>                                        27   1%
     - apply                                                       27   1%
      - #<compiled 0x1c6831>                                       27   1%
       - completion--in-region-1                                   27   1%
        - completion--do-completion                                27   1%
         - completion-try-completion                               27   1%
          - completion--nth-completion                             27   1%
           - completion--some                                      27   1%
            - #<compiled 0x1ddb305>                                27   1%
             - completion-basic-try-completion                     27   1%
              - try-completion                                     27   1%
               - #<compiled 0x1c93c9>                              27   1%
                  complete-with-action                             27   1%
- redisplay_internal (C function)                                   3   0%
 - eval                                                             3   0%
  - if                                                              3   0%
   - display-graphic-p                                              3   0%
      framep-on-display                                             3   0%


Please let me know if more information or debug data is required.


In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
 of 2018-09-06 built on the-fallen
Repository revision: 67475a59e95919e2dbe25ae950450578afdfd0dc
Windowing system distributor 'The X.Org Foundation', version 11.0.12001000
System Description: Arch Linux

Recent messages:
Package refresh done
Mark set [4 times]
Updating buffer list...
Formats have changed, recompiling...done
Updating buffer list...done
Commands: m, u, t, RET, g, k, S, D, Q; q to quit; h for help
completing-read-default: Command attempted to use minibuffer while in minibuffer
Quit [3 times]
Type C-x 1 to delete the help window, C-M-v to scroll help.
scroll-down-command: Beginning of buffer
Quit [3 times]
Configured using:
 'configure --prefix=/usr --with-sound=no --without-libsystemd
 --without-lcms2 --without-xpm --without-json --without-m17n-flt
 --without-xaw3d --without-xim --without-gpm --without-dbus
 --without-gsettings --without-selinux'

Configured features:
JPEG TIFF GIF PNG RSVG IMAGEMAGICK GLIB NOTIFY ACL GNUTLS LIBXML2
FREETYPE LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM THREADS
GMP

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

Major mode: Package Menu

Minor modes in effect:
  global-magit-file-mode: t
  diff-auto-refine-mode: t
  magit-auto-revert-mode: t
  global-git-commit-mode: t
  async-bytecomp-package-mode: t
  shell-dirtrack-mode: t
  display-battery-mode: t
  display-time-mode: t
  iswitchb-mode: t
  savehist-mode: t
  override-global-mode: t
  save-place-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  mouse-wheel-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
  column-number-mode: 1
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow flyspell ispell face-remap help-fns radix-tree ibuf-ext ibuffer
ibuffer-loaddefs mm-archive gnutls network-stream url-cache emacsbug
elec-pair mu4e-alert ht s alert log4e rx notifications dbus gntp
emms-librefm-stream emms-librefm-scrobbler emms-playlist-limit
emms-volume emms-volume-amixer emms-i18n emms-history emms-score
emms-stream-info emms-metaplaylist-mode emms-bookmarks emms-cue
emms-mode-line-icon emms-player-xine emms-player-mpd tq
emms-playing-time emms-lyrics emms-url emms-streams emms-show-all
emms-tag-editor emms-mark emms-mode-line emms-info-opusinfo
emms-info-ogginfo emms-info-mp3info emms-player-vlc emms-player-mpv
emms-player-mplayer emms-player-simple emms-info-libtag emms-browser
sort emms-playlist-sort emms-playlist-mode emms-source-playlist
emms-last-played emms-source-file locate emms-cache emms-info later-do
emms-setup emms emms-compat magit-obsolete magit-blame magit-stash
magit-bisect magit-remote magit-commit magit-sequence magit-notes
magit-worktree magit-tag magit-merge magit-branch magit-reset
magit-collab ghub-graphql ghub url-http url-gw nsm url-auth magit-files
magit-refs magit-status magit magit-repos magit-apply magit-wip
magit-log which-func imenu magit-diff smerge-mode diff-mode magit-core
magit-autorevert autorevert filenotify magit-process magit-margin
magit-mode git-commit magit-git magit-section magit-utils crm
magit-popup log-edit pcvs-util add-log with-editor async-bytecomp advice
async shell pcomplete dash mu4e-contrib mu4e desktop frameset
mu4e-speedbar speedbar sb-image ezimage dframe mu4e-main mu4e-view
cal-menu calendar cal-loaddefs thingatpt comint ansi-color mu4e-headers
mu4e-compose mu4e-context mu4e-draft mu4e-actions ido rfc2368 smtpmail
sendmail mu4e-mark mu4e-message flow-fill html2text mu4e-proc mu4e-utils
doc-view jka-compr image-mode mu4e-lists mu4e-vars message rmc rfc822
mml mml-sec epa mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader hl-line cl mu4e-meta eww mm-url gnus
nnheader gnus-util rmail rmail-loaddefs rfc2047 rfc2045 ietf-drums
mail-utils wid-edit mm-util mail-prsvr url-queue url url-proxy
url-privacy url-expand url-methods url-history url-cookie url-domsuf
url-util mailcap shr text-property-search puny svg xml dom browse-url
format-spec battery time dired-x dired dired-loaddefs edmacro kmacro
xcscope ring server iswitchb savehist bind-key easy-mmode saveplace
time-date mule-util info finder-inf package let-alist derived pcase
cl-extra help-mode easymenu url-handlers url-parse auth-source cl-seq
eieio eieio-core cl-macs eieio-loaddefs password-cache json map url-vars
seq byte-opt gv bytecomp byte-compile cconv epg epg-config subr-x
cl-loaddefs cl-lib 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 menu-bar
rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame 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 minibuffer
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 inotify
dynamic-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 1044735 82701)
 (symbols 48 40394 1)
 (strings 32 153916 8896)
 (string-bytes 1 5179292)
 (vectors 16 54258)
 (vector-slots 8 1713103 157148)
 (floats 8 190 302)
 (intervals 56 112795 946)
 (buffers 992 21))