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Re: Skipping unexec via a big .elc file

From: Eli Zaretskii
Subject: Re: Skipping unexec via a big .elc file
Date: Mon, 24 Oct 2016 16:35:08 +0300

> From: Stefan Monnier <address@hidden>
> Cc: address@hidden
> Date: Mon, 24 Oct 2016 09:04:29 -0400
> > A small price to pay for the advantages, IMO.
> I think some users will run away screaming if Emacs takes a whole second
> to start up.

It depends.  If those users, like me, have hundreds of buffers in
their sessions, and use desktop.el to recreate their sessions, they
already wait a few seconds for that.

And I don't expect the result to be 1 sec, that's is a rounded up
value that is already higher than what I saw.

> > The most important advantage in my view is that the dumping/loading
> > process becomes very simple and understandable even by people with
> > minimal knowledge of C subtleties and Emacs internals,
> Yes, the benefits are clear, but the cost is pretty steep.

We will have to speed this up, of course.  You didn't expect tossing
unexec to be an easy job, did you?

> I think we could live with a 0.2s startup time, but that's already
> a pretty high cost:
> - 0.2s feels sluggish when you expect "immediate".
> - byte-compilation has historically moved from "do it in a single
>   session", to "start a separate Emacs session for each file" for good
>   reasons.  A 0.2s startup time imposes either a much slower
>   byte-compilation, or will compel us to go back to "do it all in
>   a single session".

I think you forget parallelism.  We build Emacs with several
compilations running in parallel for a long time.  And byte-compiling
a typical file already takes more than 0.2 sec, sometimes (often?)
significantly more, so I don't see a catastrophe yet.

> > This would make future maintenance much more robust and reliable, and
> > also allow more contributors to work on improving, speeding up, and
> > extending the build process.  The alternatives all require us to
> > depend on a dwindling handful of people, which is a huge disadvantage
> > in the long run.
> Maybe there's indeed a lot of speed up still waiting there, and by
> reducing loading time of .elc files (and/or allowing more laziness there)
> we could bring down the 0.96s to 0.2s *and* speed up other uses at the
> same time.

That's my hope, yes.  E.g., maybe reading the startup.elc file could
run in another thread?

In any case, I don't think it's right to throw out this idea without
trying very hard to make it work, because the benefits are so clear.

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