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Re: Altivec in baseline for ppc64?

Hi Sébastien,

On Tue, Jul 13, 2021 at 2:04 PM Sébastien Villemot <sebastien@debian.org> wrote:
> Hi,
> The wiki page that synthesizes architecture specificities indicates
> that Altivec is included in the baseline for the ppc64 port:
> https://wiki.debian.org/ArchitectureSpecificsMemo#ppc64
> However my understanding is that this port supports any powerpc64 CPU,
> including some that don’t have Altivec (e.g. POWER4 or POWER5). This is
> also what the main wiki page for PPC64 says:
> https://wiki.debian.org/PPC64
> Can someone please clarify the situation?
> (I’m asking because I’m the maintainer of the openblas package, and
> knowing whether Altivec is available or not, and more generally what is
> in the baseline, is essential for proper packaging).

I do not believe that you can do much as a packager. You cannot assume
anything on the target arch. You need to do the same thing as ffmpeg
is doing for avx2/sse4 on amd64, you need to do runtime detection. So
unless upstream is doing something very clever you cannot compile blas
using any of the fancy altivec instructions :(

The man page for ld.so mentions something about optimized libraries
(search for "/usr/lib/sse2/"), but this is currently not in use in
Debian (AFAIK).


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