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

* Masahiro Yamada <yamada.masahiro@socionext.com> 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@socionext.com>
> ---
>
> 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@kernel.org>

Thanks,

Ingo

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