Re: [gentoo-dev] [PATCH 6/8] kernel-build.eclass: compress xz/zstd in parallel

["Michał Górny" <mgorny@gentoo.org>]

On Tue, 2022-10-11 at 23:54 +0100, Sam James wrote:
> Note that this will only take effect if compressing
> modules with xz or zstd (COMPRESS_MODULE_XZ is set or
> COMPRESS_MODULE_ZSTD is set respectively)
> 
> ... or if compiling the kernel with xz or zstd (COMPRESS_KERNEL_XZ
> or COMPRESS_KERNEL_ZSTD is set respectiely).
> 
> Signed-off-by: Sam James <sam@gentoo.org>
> ---
>  eclass/kernel-build.eclass | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/eclass/kernel-build.eclass b/eclass/kernel-build.eclass
> index 98a385bf72c0..936258e9e8af 100644
> --- a/eclass/kernel-build.eclass
> +++ b/eclass/kernel-build.eclass
> @@ -29,7 +29,7 @@ esac
>  
>  PYTHON_COMPAT=( python3_{8..11} )
>  
> -inherit python-any-r1 savedconfig toolchain-funcs kernel-install
> +inherit multiprocessing python-any-r1 savedconfig toolchain-funcs kernel-install
>  
>  BDEPEND="
>  	${PYTHON_DEPS}
> @@ -90,6 +90,14 @@ kernel-build_src_configure() {
>  		ARCH=$(tc-arch-kernel)
>  	)
>  
> +	if type -P xz ; then
> +		export XZ_OPT="-T$(makeopts_jobs)"
> +	fi
> +
> +	if type -P zstd ; then
> +		export ZSTD_NBTHREADS="$(makeopts_jobs)"
> +	fi
> +
>  	restore_config .config
>  	[[ -f .config ]] || die "Ebuild error: please copy default config into .config"
>  

I'm think that we need an override for these values.  Just because
someone is using -j12 to compile source files in parallel (which has no
real drawback), it doesn't mean that that person wants to use 12-thread
parallel xz/zstd that will actually reduce compression ratio for minimal
gain (I mean, most of these files won't even use parallel compression
because they're too small).

Not to mention that someone using -j32 distcc setup necessarily wants
32-threaded local compression.

-- 
Best regards,
Michał Górny