linux-kernel - Re: [PATCH v3 1/1] kbuild: deb-pkg: Build parallely with current dpkg-buildpackage

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Date:   Tue, 21 Mar 2023 19:18:32 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Bastian Germann <bage@...utronix.de>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] kbuild: deb-pkg: Build parallely with current dpkg-buildpackage

On Thu, Mar 16, 2023 at 2:35 AM Bastian Germann <bage@...utronix.de> wrote:
>
> With dpkg-buildpackage v1.21.10 or later, the only way to build the
> deb-pkg generated package parallely is adding -j<N> to the MAKEFLAGS
> environment variable or using the --jobs-force option, see dpkg commit
> 1d0ea9b2ba3f ("dpkg-buildpackage: Change -j, --jobs semantics to
> non-force mode"). The package ignores the usual parallel build option
> that is described in Debian Policy.
>
> Derive make's -j parameter from the DEB_BUILD_OPTIONS environment variable
> that ends up being set by dpkg-buildpackage -j<N>. The snippet is copied
> from Debian Policy.
>
> Link: https://www.debian.org/doc/debian-policy/ch-source.html#debian-rules-and-deb-build-options
> Signed-off-by: Bastian Germann <bage@...utronix.de>
> ---


I was about to pick this up, then I stopped it.



If I apply this patch,

"make -j2 bindeb-pkg" shows a new warning.

make[3]: warning: -j16 forced in makefile: resetting jobserver mode.




Please note `nproc` returns 16 on my machine.


"make bindeb-pkg" also runs in 16 threads because
$(DEB_BUILD_OPTIONS) always contains "parallel=16"
even if -j<N> option is given at all.

In other words, this patch will take away user's freedom
to choose the number of threads.









>  scripts/package/mkdebian | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/scripts/package/mkdebian b/scripts/package/mkdebian
> index f74380036bb5..ed5c2b65798b 100755
> --- a/scripts/package/mkdebian
> +++ b/scripts/package/mkdebian
> @@ -238,6 +238,11 @@ fi
>  cat <<EOF > debian/rules
>  #!$(command -v $MAKE) -f
>
> +ifneq (,\$(filter parallel=%,\$(DEB_BUILD_OPTIONS)))
> +       NUMJOBS = \$(patsubst parallel=%,%,\$(filter parallel=%,\$(DEB_BUILD_OPTIONS)))
> +       MAKEFLAGS += -j\$(NUMJOBS)
> +endif
> +
>  srctree ?= .
>
>  build-indep:
> --
> 2.39.2
>


-- 
Best Regards
Masahiro Yamada