Re: master 289000e: Merge branch 'feature/native-comp' into trunk

[Alan Mackenzie]

Hello, Eli.

On Mon, Apr 26, 2021 at 14:40:11 +0300, Eli Zaretskii wrote:
> > Date: Sun, 25 Apr 2021 21:55:29 +0000
> > Cc: akrl@sdf.org, emacs-devel@gnu.org
> > From: Alan Mackenzie <acm@muc.de>

> > > > What else do I need to know, successfully to build and run the
> > > > native compilation feature?

> > > Hopefully, nothing (just to build and run).

> > This is sadly far from true.  You need to know basic things like native
> > compile files are .eln.  You need to know how to compile files.  I
> > guessed that

> >     $ emacs -Q -batch -f batch-native-compile lisp/progmodes/cc-*.el

> > would natively compile CC Mode.

> You originally said nothing about compiling any Lisp files, let alone
> measuring the performance of CC Mode as result of native-compilation.
> The answer I gave specifically said "just to build and run".

OK, fair enough!  ;-)

> Indeed, for your purpose, one needs to do more.

> > Well, it took several minutes of processing in which it did
> > something, but I don't know what.  A find failed to find
> > '*cc-*.eln'.

> I believe they should be under your ~/.emacs.d/eln-cache/ directory.

They are indeed there, yes.  Thanks.

> > On restarting Emacs, my favourite CC Mode benchmark was only
> > marginally (~4%) faster.

> I'm guessing that you didn't compile everything you need natively.  It
> is quite hard to determine "by hand" which Lisp files will be needed,
> as CC Mode files use Lisp code from many other files, and they all
> need to be natively-compiled to see the full benefits.

> My suggestion is to load and run the code you want to benchmark, but
> after the benchmark finishes, leave Emacs running until 'ps' no longer
> shows inferior Emacs processes run in the background -- those are the
> subprocesses Emacs starts to natively-compile every .el file your
> program loads.  Once all the native-compilation subprocesses exit,
> exit your interactive session, and then run the benchmark again; this
> time it should show the full speedup of native-compilation.

I've tried that, but I don't think the native compile versions of CC Mode
got loaded.  If they had been loaded, there would have been _some_ speed
up.  What I did was, in essence,

    M-: (load-file "~/emacs/emacs.git/master/lisp/progmodes/cc-defs.elc")

(but from a Lisp script), repeated ~thirteen times for each CC Mode file.
This didn't seem to load the corresponding cc-defs-....eln, etc.  Should
it?  If not, what is the canonical way to load a set of .eln files?  Do I
have to give the exact .eln file names in the load-file calls?  Or, am I
forced to tweak load-path to load a specific natively compiled version of
CC Mode?  How do I know when a .eln file has been loaded?

> > I'm frustrated at the moment.  I want to use this new feature, but don't
> > know how to, and can't find any documentation.  "native compilation"
> > doesn't seem to appear in either the Emacs or the Elisp manual.

> We have a lot to do in the documentation department for this feature.
> You can wait until we are done (which could take a while), or you
> could ask questions (but in the latter case please be more specific,
> so that the answers are useful for you).

Sorry, I got the impression that, with the merge, the feature was almost
ready for full time use in Emacs.  Maybe I should be patient and wait a
little longer.

Thanks for the help!

-- 
Alan Mackenzie (Nuremberg, Germany).