Fax/PDF performance regression compared to focal

Stephan: My suggestion would be to try to reproduce this upstream and file an issue with them so this can get fixed, as this is a community-maintained package.

if it helps for testing upstream the package build option are defined there, https://salsa.debian.org/debian/imagemagick/-/blob/master/debian/rules#L70

Thanks to Sebastien and Julian for the hints. There seem to have been some performance variation in upstream around 6.9.10...6.9.11, but never quite as bad as the Ubuntu package.

Steps taken:

$ sudo apt-get build-dep imagemagick-6.q16
$ git clone https://github.com/ImageMagick/ImageMagick6.git
$ cd ImageMagick6
$ git checkout 6.9.11-60
$ ./configure --prefix=/usr/local/stow/ImageMagick6 --with-modules --with-gs-font-dir=/usr/share/fonts/type1/gsfonts -with-magick-plus-plus --with-djvu --with-heic --with-openjp2 --with-webp --with-wmf --without-gvc --without-dps --without-fpx --with-perl --without-rsvg --with-fftw
$ make
$ sudo make install
$ cd /usr/local/stow
$ sudo stow ImageMagick6
$ sudo ldconfig
$ cd ~
$ time /usr/local/bin/convert -version scan.pnm -compress Fax scan-upstream.pdf
Version: ImageMagick 6.9.11-60 Q16 x86_64 2021-01-24 https://imagemagick.org
Copyright: (C) 1999-2021 ImageMagick Studio LLC
License: https://imagemagick.org/script/license.php
Features: Cipher DPC Modules OpenMP(4.5)
Delegates (built-in): bzlib djvu fftw fontconfig freetype heic jbig jng jp2 jpeg lcms lqr ltdl lzma openexr pangocairo png tiff webp wmf x xml zlib

real 0m10.906s
user 0m11.559s
sys 0m0.829s

This is slower than I had on Focal, I believe it was around 5 seconds but I don't have measurements. Unstow it and I'm back at 4m44s:

$ cd /usr/local/stow
$ sudo stow -D ImageMagick6
$ sudo ldconfig
$ cd ~
$ time /usr/bin/convert -version scan.pnm -compress Fax scan-ubuntu.pdf
Version: ImageMagick 6.9.11-60 Q16 x86_64 2021-01-25 https://imagemagick.org
Copyright: (C) 1999-2021 ImageMagick Studio LLC
License: https://imagemagick.org/script/license.php
Features: Cipher DPC Modules OpenMP(4.5)
Delegates (built-in): bzlib djvu fftw fontconfig freetype heic jbig jng jp2 jpeg lcms lqr ltdl lzma openexr pangocairo png tiff webp wmf x xml zlib

real 4m43.623s
user 2m6.014s
sys 2m38.471s
$ ls -la scan-*.pdf
-rw-rw-r-- 1 i i 127070 Okt 15 16:35 scan-ubuntu.pdf
-rw-rw-r-- 1 i i 127046 Okt 15 16:29 scan-upstream.pdf

Configuring the package resulted in the following:

==============================================================================
ImageMagick 6.9.11-60 is configured as follows. Please verify that this
configuration matches your expectations.

Host system type: x86_64-pc-linux-gnu
Build system type: x86_64-pc-linux-gnu

                  Option Value
------------------------------------------------------------------------------
Shared libraries --enable-shared=yes yes
Static libraries --enable-static=yes yes
Module support --with-modules=yes yes
GNU ld --with-gnu-ld=yes yes
Quantum depth --with-quantum-depth=16 16
High Dynamic Range Imagery
                  --enable-hdri=no no

Install documentation: yes

Memory allocation library:
  JEMalloc --with-jemalloc=no no
  TCMalloc --with-tcmalloc=no no
  UMem --with-umem=no no

Delegate library configuration:
  BZLIB --with-bzlib=yes yes
  Autotrace --with-autotrace=no no
  DJVU --with-djvu=yes yes
  DPS --with-dps=no no
  FFTW --with-fftw=yes yes
  FLI...

Ubuntu 22.10 (Kinetic Kudu) has reached end of life, so this bug will not be fixed for that specific release.