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

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

[Gregor Zattler]

Hello,

among several runs of

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?


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

[Eli Zaretskii]

> 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.

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

[John Yates]

I work on a product whose structure involves literally hundreds of
DLLs / SOs.  We tolerate slow start-up in-house because it optimizes
the compile / edit / debug cycle.

Packaging the final product involves an extra step to collapse our
hundreds of images into just a handful via a secondary link step.
I wonder if there is anything analogous that Emacs could do.

/john

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

[Eli Zaretskii]

> From: John Yates <john@yates-sheets.org>
> Date: Thu, 26 Jan 2023 20:16:36 -0500
> 
> I work on a product whose structure involves literally hundreds of
> DLLs / SOs.  We tolerate slow start-up in-house because it optimizes
> the compile / edit / debug cycle.

How many hundreds?  Emacs 29 loads almost 300 *.eln files at startup.

> Packaging the final product involves an extra step to collapse our
> hundreds of images into just a handful via a secondary link step.
> I wonder if there is anything analogous that Emacs could do.

I'm not sure this is possible with loading natively-compiled Lisp in
Emacs, because there are some unique conditions and requirements in
our case, like the need to be able to run both installed and
un-installed Emacs, find the correct *.eln files on the system, etc.
It isn't like loading a shared library from a system-wide directory
where shared libraries live.

In any case, please start a discussion about this on emacs-devel, and
please CC Andrea Corallo <akrl@sdf.org>, who developed the native
compilation and tried several alternatives for dumping Emacs with
natively-compiled Lisp before arriving at what we do today.  It's a
complex problem with many facets.