[luatex] Identifying why LuaTeX 2023 is slower than LuaTeX 2022

[Reinhard Kotucha]

On 2023-08-29 at 15:38:35 +0200, Hans Hagen wrote:

 > So guess what: as i mentioned before there has been a discussion about
 > portable fmt files (irr a latex request) and the normal luatex build
 > script has --no-dump-share but araiks tex live doesn't do that (any
 > longer) so then we get 0.020 sec per run more (2+ sec on 100 runes).
 >
 > (plain has a very small format so one can wonder if it's the same there
 > as in other macropackages)

Hi Hans,
as far as plain TeX is concerned, I don't think that the endianmess is
the main problem.  As of 2016 TeX Live loads the file UnicodeData.txt
(1.9 MB) into the format file.

If you remove the line

  \input load-unicode-data.tex

from luatex.ini you probably save much more time than with
--disable-dump-share.

 > Of course there can be other factors in a non context universe like the
 > time needed to load a file database (wasn't there a upper / lowercase
 > checking change recently?), fonts etc.

There are currently more than 200,000 files in texmf-dist.  I've
written a script based on strace(1) which creates a tiny subset of TeX
Live in another directory containing only the files needed to process
that particular document.  It's invoked like this:

   tinytex luatex myfile.tex

When I compile a plain TeX document this way the tiny TeX distribution
created by my script usually contains less than 30 files.

Kpathsea needs a bit more time to locate files within a system
containing 200,000 files than within a system containing only 30 files.
The difference is measurable but negligible.  Kpathsea is extremely
fast.

 > Then when we talk macro packages,

We shouldn't.  If we are interested in the speed of an *engine* we
have to avoid macro packages and LaTeX by all means.  LaTeX introduces
too many rooms of freedom and is a moving target.

For benchmarking it's best to stick with plain TeX.  It's pretty easy
to create a 500+ pages lorem ipsum with a halfways reasonable text
editor.

Regards,
  Reinhard

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Reinhard Kotucha                            Phone: +49-511-3373112
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