Re: Emacs build times on Windows

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 21 Apr 2012 06:05:42 -0600
> From: Christoph Scholtes <cschol2112@googlemail.com>
> CC: emacs-devel@gnu.org
> 
> > On my i7 desktop (4 hyper-threaded cores), it takes 9 minutes, if I
> > use the -j10 switch to Make.  I suggest that you try -j6 in your
> > builds (if you use anything older than the current CVS of GNU Make,
> > you will also have to use the XMFLAGS="-j6" kludge as well, see
> > nt/INSTALL).  A parallel build should be faster.
> 
> Thanks. Does this work with mingw32-make also or do I have to use Cygwin 
> (or MSYS?) to obtain gmake?

Parallel builds are supported by the native Windows build of GNU Make
since v3.81.  So if you have mingw32-make v3.81 or 3.82, you should be
all set for parallelism.

> I tried building with mingw32-make -j2 but it did not result in any 
> significant speedup.

Like I said: you need to say "mingw32-make -j2 XMFLAGS=-j2" for this
to work.

The issue here is that the native Windows build of Make does not yet
support the "job server" method of parallel execution, which causes
the number of jobs in each sub-Make be reset to 1.  The XMFLAGS=-j2
kludge works around that by forcing the sub-Make's to use an explicit
"-jN" switch.

(The current CVS code of Make includes a job server implementation for
Windows, so the next release of Make will free us from this kludge.)

> > IOW, we use a shell-level loop to compile the files one by one.
> >
> > So if you are looking for the place to significantly speed up the
> > bootstrap, the first place to look is to make the byte compilation use
> > a similar setup to what you see in lisp/Makefile.in.
> 
> I see. I will look into that. Thanks.

Thanks in advance.