Re: [gentoo-dev] Augmenting the CPU_FLAGS_X86 list and creating CPU_FLAGS_PPC + CPU_FLAGS_ARM

[Mart Raudsepp]

Ühel kenal päeval, T, 02.08.2016 kell 15:25, kirjutas Michał Górny:
> On Mon, 1 Aug 2016 17:15:41 -0400
> Mike Gilbert <floppym@g.o> wrote:
>
> > On Mon, Aug 1, 2016 at 5:08 PM, David Seifert <soap@g.o>
> > wrote:
> > > Dear friends,
> > > while version bumping sci-libs/fftw, I've noticed our
> > > CPU_FLAGS_X86
> > > list could be expanded a bit:
> > >
> > > avx512 - introduced with Skylake and Knights Landing
> >
> > According to Wikipedia, "AVX-512 consists of multiple extensions
> > not
> > all meant to be supported by all processors implementing them."
> >
> > https://en.wikipedia.org/wiki/AVX-512
> >
> > https://en.wikipedia.org/wiki/CPUID#EAX.3D7.2C_ECX.3D0:_Extended_Fe
> > atures
>
> Also https://bugs.gentoo.org/show_bug.cgi?id=588628.

Do we actually want to be fast in adding these things, or do we want to
wait for any actual consumers to be possible to start consuming it
right away? Like with all these different variants, will consumers
actually group the variants in the same way and will we be able to map
things cleanly in ebuilds in the future?
Though I guess there are already potential consumers out there that
people have already looked at and I've just not kept up with IRC or
something :)

Also, how are they exposed in cpuinfo, do we have first patches
for cpuid2cpuflags? Since what kernel version are they exposed in
cpuinfo, is it a flag for each CPUID capability? What variants do each
CPU implementing any expose, maybe all CPUs doing e.g avx512f all also
do avx512dq - perhaps all consumers would make such assumptions and
assume things based on real world CPUs? Or maybe all consumers of some
of the variants will always do runtime detection themselves and we
won't even use that flag in an IUSE ever?

tl;dr: Concerned about prematurely adding things without knowing of
consumer examples


Mart