Re: [PATCH 3/4] kbuild: create object directories simpler and faster

[Ingo Molnar]

* Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> wrote:

> For the out-of-tree build, scripts/Makefile.build creates output
> directories, but this operation is not efficient.
> 
> scripts/Makefile.lib calculates obj-dirs as follows:
> 
>   obj-dirs := $(dir $(multi-objs) $(obj-y))
> 
> Please notice $(sort ...) is not used here.  Usually the resulted
> obj-dirs is as many "./" as objects.
> 
> For those duplicated paths, the following command is invoked.
> 
>   _dummy := $(foreach d,$(obj-dirs), $(shell [ -d $(d) ] || mkdir -p $(d)))
> 
> Then, the costly shell command is run over and over again.
> 
> I see many points for optimization:
> 
> [1] Use $(sort ...) to cut down duplicated paths before passing them
>     to system call
> [2] Use single $(shell ...) instead of repeating it with $(foreach ...)
>     This will reduce forking.
> [3] We can calculate obj-dirs more simply.  Most of objects are already
>     accumulated in $(targets).  So, $(dir $(targets)) is fine and more
>     comprehensive.
> 
> I also removed bad code in arch/x86/entry/vdso/Makefile.  This is now
> really unnecessary.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> ---
> 
>  arch/x86/entry/vdso/Makefile |  4 ----
>  scripts/Makefile.build       | 15 ++++++---------
>  scripts/Makefile.host        | 11 -----------
>  scripts/Makefile.lib         |  5 -----
>  4 files changed, 6 insertions(+), 29 deletions(-)

I love not just the speedup, but the diffstat as well ;-)

Acked-by: Ingo Molnar <mingo@xxxxxxxxxx>

Thanks,

	Ingo