Re: emacs empty startup time increased from v 27.1 to 29.0 by factor 3?

[Gregor Zattler]

Hi Eli, emacs users,
* Eli Zaretskii <eliz@gnu.org> [2023-01-23; 17:08 +02]:
>> From: Gregor Zattler <telegraph@gmx.net>
>> Date: Mon, 23 Jan 2023 15:08:15 +0100
>>
>> time /usr/bin/emacs-gtk -Q -nw -f save-buffers-kill-emacs
>>
>> which starts emacs 27.1 as precompiled in debian / Bullseye
>> and kills it again, a low time values on my laptop are e.g.:
>>
>> real    0m0,328s
>> user    0m0,262s
>> sys     0m0,058s
>>
>>
>> while for emacs v29.0 the same command line achives low
>> values like this one:
>>
>> real    0m1,007s
>> user    0m0,847s
>> sys     0m0,154s
>>
>> The 29.0 version is compiled with native-compilation
>> support.  Does this explain the differences?
>
> It could.  Emacs with native-compilation needs to load all the
> preloaded Lisp packages as shared libraries, as opposed to just
> mapping the pdumper file into the address space in Emacs 27.  To be
> sure, build Emacs 29 without native-compilation, and then compare.

So I did.  The lowest values for the same command with a
slightly newer Version which was built with --with-native-compilation=no
are:


$ time src/emacs -Q -nw -f save-buffers-kill-emacs

real    0m0,596s
user    0m0,483s
sys     0m0,105s


while the very same tree build  with --with-native-compilation

$ time src/emacs -Q -nw -f save-buffers-kill-emacs

real    0m1,082s
user    0m0,902s
sys     0m0,169s

This shows: a) native compilation slows Emacs' startup (and
shutdown?).  b) Without native compilation support Emacs
27.1 is faster in this nano-benchmark than Emacs 29.0.


Ciao; Gregor
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