Parallel builds

[Ian Lynagh]

On Sun, Sep 09, 2007 at 11:58:26AM +0200, Sven Panne wrote:
> On Saturday 08 September 2007 19:33, Stefan O'Rear wrote:
> > [...]
> > $(MAKE) always includes the flags (at least with gnumake), cf "info make
> > MAKE\ Variable".
> 
> Nope... Don't stop reading manuals prematurely: ;-)
> 
>   http://www.gnu.org/software/make/manual/html_node/Options_002fRecursion.html

I'm not sure exactly which bit of that URL you're referring to?

> Easy test:
> 
> ---------- Makefile --------------------------------------
> subsystem:
> 	@echo "top MAKE      = $(MAKE)"
> 	@echo "top MAKEFLAGS = $(MAKEFLAGS)"
> 	@echo "top MFLAGS    = $(MFLAGS)"
> 	cd subdir && $(MAKE)
> ----------------------------------------------------------
> 
> ---------- subdir/Makefile -------------------------------
> all:
> 	@echo "sub MAKE      = $(MAKE)"
> 	@echo "sub MAKEFLAGS = $(MAKEFLAGS)"
> 	@echo "sub MFLAGS    = $(MFLAGS)"
> ----------------------------------------------------------
> 
> ---------- output ----------------------------------------
> panne at spock:~/maketest> make -j2 foo=bar
> top MAKE      = make
> top MAKEFLAGS =  --jobserver-fds=3,4 -j -- foo=bar
> top MFLAGS    = - --jobserver-fds=3,4 -j
> cd subdir && make
> make[1]: Entering directory `/home/panne/maketest/subdir'
> sub MAKE      = make
> sub MAKEFLAGS = w --jobserver-fds=3,4 -j -- foo=bar
> sub MFLAGS    = -w --jobserver-fds=3,4 -j
> make[1]: Leaving directory `/home/panne/maketest/subdir'
> ----------------------------------------------------------

What is this test meant to show? That -j is being passed down correctly,
so it works as-is?

> So MAKEFLAGS seems to be passed down automatically, but I think that we still 
> have to mention it in the recursive call.

Why do you think that?

> We do this already for every 
> directory in SUBDIRS_BUILD, but that doesn't include "libraries". (Well, we 
> use MFLAGS there, which should probably better be MAKEFLAGS, BTW).

The URL you give says, in relation to using "$(MAKE) $(MFLAGS)",

    [...] MAKEFLAGS makes this usage redundant. If you want
    your makefiles to be compatible with old make programs, use this
    technique [...]

IIRC on *BSD you need to use gmake rather than make to build GHC, so I
doubt that any such "old make programs" can build GHC anyway. Even if
they can, the build will still work, just with less parallelisation.


Thanks
Ian