Re: [Buildroot] [PATCH 1/1] core: Use of percent_defconfig seems to impact performance

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

Nevo, All,

On 2023-01-04 20:57 -0500, Nevo Hed via buildroot spake thusly:
> Noticed a significant slowdown with rise of number of external trees
> in our env.  This slowdown seemed to be related to invocations if the
> percent_defconfig function (GNU Make 4.3).
> 
> While I have not do a deep dive in analyzing the performance issue, it
> felt like redefining the %_defconfig rule N times impact performance.
> 
> This patch makes %_defconfig a single rule which combines uses the
> first return of a wildcard expression.
> 
> Timing (seconds) of `make pc_x86_64_bios_defconfig` with 1-8 external
> trees:
> 
>     #Trees    Before    After
>          1      0.38     0.37
>          2      0.32     0.31
>          3      0.31     0.33
>          4      0.36     0.32
>          5      0.45     0.35
>          6      1.26     0.36
>          7      9.10     0.36
>          8     85.93     0.42
> 
> Signed-off-by: Nevo Hed <nhed+buildroot@starry.com>

Thanks for the respin, I like it better than your first iteration, and
most importantly, better than my own implementation!

I however used most of my commit log, a=exteneded it even further,
provided my reproducibility script in the commit log and redid the
timings up to 1000 trees (heck, it's manageable now, so why not!).

I also slightly reformatted the code, to split the long lines.

Finally, I also added David as the reporter, and that his bug #14996
is now fixed.

Applied to master, thanks.

Regards,
Yann E. MORIN.

> ---
>  Makefile | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 88f90cd2fa..ad866f1f24 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1013,13 +1013,14 @@ oldconfig syncconfig olddefconfig: $(BUILD_DIR)/buildroot-config/conf outputmake
>  defconfig: $(BUILD_DIR)/buildroot-config/conf outputmakefile
>  	@$(COMMON_CONFIG_ENV) $< --defconfig$(if $(DEFCONFIG),=$(DEFCONFIG)) $(CONFIG_CONFIG_IN)
>  
> -define percent_defconfig
> -# Override the BR2_DEFCONFIG from COMMON_CONFIG_ENV with the new defconfig
> -%_defconfig: $(BUILD_DIR)/buildroot-config/conf $(1)/configs/%_defconfig outputmakefile
> -	@$$(COMMON_CONFIG_ENV) BR2_DEFCONFIG=$(1)/configs/$$@ \
> -		$$< --defconfig=$(1)/configs/$$@ $$(CONFIG_CONFIG_IN)
> -endef
> -$(eval $(foreach d,$(call reverse,$(TOPDIR) $(BR2_EXTERNAL_DIRS)),$(call percent_defconfig,$(d))$(sep)))
> +%_defconfig: $(BUILD_DIR)/buildroot-config/conf  outputmakefile
> +	@defconfig=$(or \
> +		$(firstword $(foreach d, \
> +			$(call reverse,$(TOPDIR) $(BR2_EXTERNAL_DIRS)),$(wildcard $(d)/configs/$@))), \
> +		$(error "Can't find $@") \
> +	); \
> +	$(COMMON_CONFIG_ENV) BR2_DEFCONFIG=$${defconfig} \
> +		$< --defconfig=$${defconfig} $(CONFIG_CONFIG_IN)
>  
>  update-defconfig: savedefconfig
>  
> -- 
> 2.38.1
> 
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