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

[Sam James <sam@gentoo.org>]

> On 12 Oct 2022, at 05:46, Michał Górny <mgorny@gentoo.org> wrote:
> 
> 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.

I'll make it use XZ_OPT if present in environment to avoid clobbering, ditto zstd.