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

From: Lynn Winebarger
Subject: Re: emacs empty startup time increased from v 27.1 to 29.0 by factor 3?
Date: Sat, 28 Jan 2023 04:00:53 -0500

Hi, John,
The closest thing in Emacs to what you describe is dumping, which currently isn't supported for native compilation, unless something has changed that I'm not aware of.
Last summer I did an experiment and modified 28.1 to support dumping native compilation.  I had a startup that was loading all libraries included with emacs and approximately an additional 1000 packages installed in site-lisp (lots of manual modifications to make that happen).
Loading those packages at startup as regular packages, after ensuring all were compiled ahead of time, increased startup time to 15 minutes or more. The dumped version only took 5 seconds or so.
I discarded that experiment, but have done a similar site-lisp installation with maybe half of those additional packages.  The dump produced by "dump-emacs-portable" starts almost instantly.  Even without dumping, startup time is only 30 seconds or so.  For that matter, it takes 12 minutes to dump the byte-compiled function, where dumping the natively compiled version would take over 30 minutes.  It's not a completely fair comparison since (if memory serves) the natively compiled version loaded 4000-5000 files where this version is only loading ~2200 libraries.

Loading natively compiled libraries does do some additional checking to compare source file to the compiled library by checksum.  Maybe that's part of the 3x you're seeing?


On Fri, Jan 27, 2023, 12:22 PM John Yates <john@yates-sheets.org> wrote:
Reposting to emacs-devel at Eli's behest.

Re my suggested parallel, Eli asked:

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

I have never needed to answer that question.

I work on the code generation middle-end.  When I modify one of its
fundamental headers over 350 modules get rebuilt.  (That number
reflects poor dependency management, which is being addressed.)
There are probably just as many modules unrelated to code generation
(e.g. UI, graphics, etc).

---------- Forwarded message ---------
From: John Yates <john@yates-sheets.org>
Date: Thu, Jan 26, 2023 at 8:16 PM
Subject: Re: emacs empty startup time increased from v 27.1 to 29.0 by factor 3?
To: <help-gnu-emacs@gnu.org>

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.

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