[Buildroot] [PATCH v2] Makefile: add --no-builtin-rules flag

[Yann E. MORIN <yann.morin.1998@free.fr>]

Arnout, All,

On 2016-03-12 00:47 +0100, Arnout Vandecappelle (Essensium/Mind) spake thusly:
> When calling 'make', it takes several seconds before anything happens.
> This is because all the makefiles that have to be parsed and variables
> and rules that have to be evaluated.
> 
> One of the rules to be evaluated are the implicit rules that make adds
> to check out the *.mk files from RCS etc. This obviously makes no
> sense. Therefore, disable the built-in rules.
> 
> To avoid breaking package that depend on them, make sure we filter this
> out when calling sub-makes. MFLAGS has to be overridden too, otherwise
> the sub-make will just use that instead of MAKEFLAGS when MAKEFLAGS is
> empty.
> 
> Time for 'make help > /dev/null' on my machine (with hot cache):
>          before      after
> real    0m4.167s   0m3.375s
> user    0m3.596s   0m2.928s
> sys     0m0.256s   0m0.180s
> 
> and for 'make graph-depends' on a large config:
>          before      after
> real    0m58.417s  0m53.625s
> user    0m48.284s  0m43.680s
> sys     0m4.076s   0m3.536s
> 
> A roughly 10% improvement.
> 
> Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
> ---
> v2: override MFLAGS as well.
> ---
>  Makefile            | 2 ++
>  package/Makefile.in | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index f2822a2..bbb2017 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -29,6 +29,8 @@ UMASK = 0022
>  ifneq ($(shell umask),$(UMASK))
>  .PHONY: _all $(MAKECMDGOALS)
>  
> +%.mk:
> +
>  $(MAKECMDGOALS): _all
>  	@:
>  
> diff --git a/package/Makefile.in b/package/Makefile.in
> index fbf5485..730810e 100644
> --- a/package/Makefile.in
> +++ b/package/Makefile.in
> @@ -1,3 +1,4 @@
> +MAKEFLAGS += --no-builtin-rules
>  ifndef MAKE
>  MAKE := make
>  endif
> @@ -5,6 +6,7 @@ ifndef HOSTMAKE
>  HOSTMAKE = $(MAKE)
>  endif
>  HOSTMAKE := $(shell which $(HOSTMAKE) || type -p $(HOSTMAKE) || echo make)
> +HOSTMAKE += MAKEFLAGS="$(filter-out --no-builtin-rules,$(MAKEFLAGS))" MFLAGS=

Is the extra added complexity worth the improvement?

Regards,
Yann E. MORIN.

>  # If BR2_JLEVEL is 0, scale the maximum concurrency with the number of
>  # CPUs. An additional job is used in order to keep processors busy
> -- 
> 2.7.0
> 
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