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Re: Two strange messages while building Emacs on MS-Windows

From: Eli Zaretskii
Subject: Re: Two strange messages while building Emacs on MS-Windows
Date: Sat, 08 Dec 2012 11:24:16 +0200

> Date: Sat, 8 Dec 2012 09:43:22 +0100
> From: Dani Moncayo <address@hidden>
> Cc: address@hidden
> I'll try a parallel build.  BTW, a plain "-j" option seem to be a good
> choice;  according to the GNU Make manual it will dynamically
> determine how many parallel recipes can be run:
>   `-j [JOBS]'
>   `--jobs[=JOBS]'
>        Specifies the number of recipes (jobs) to run simultaneously.
>        With no argument, `make' runs as many recipes simultaneously as
>        possible.  If there is more than one `-j' option, the last one is
>        effective.  *Note Parallel Execution: Parallel, for more
>        information on how recipes are run.  Note that this option is
>        ignored on MS-DOS.

Read more.  In the referenced node, the manual says:

     If the `-j' option is followed by an integer, this is the number of
  recipes to execute at once; this is called the number of "job slots".
  If there is nothing looking like an integer after the `-j' option,
  there is no limit on the number of job slots.

That's it.  Nothing as sophisticated as you seem to have concluded.
On Windows, "no limit" means "-j 64", because that's the limitation of
the API used on Windows to watch child processes.

(The referenced node also describes the -l option, which could limit
the effective number of parallel jobs depending on the system load,
but since sensing the system load doesn't work on Windows, that option
is of no use for you.)

So I suggest to time different "-j N" bootstraps and find the one that
is the fastest.  Or just use the recipe I gave ;-)

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