Re: x86_64-v2 in Fedora

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On Tue, Jun 15, 2021 at 5:50 PM Fabio Valentini <decathorpe@xxxxxxxxx> wrote:
>
> On Tue, Jun 15, 2021 at 11:35 PM Neal Gompa <ngompa13@xxxxxxxxx> wrote:
> >
> > Hey all,
> >
> > Earlier this week, I was helping with processing features for openSUSE
> > Leap 15.4[1] and I discovered that they're planning on introducing
> > x86_64-v2 to openSUSE soon. The reference for this change was that
> > RHEL 9 is going to use x86_64-v2[2]. Additionally, other distributions
> > have been considering bumping up to v2 or v3[3][4].
> >
> > Some cursory examination of the new x86_64 sublevels seem to indicate
> > that x86_64-v2 goes back to roughly 2007~2008, merely cutting off the
> > first couple of generations of x86_64 CPUs from Intel and AMD. I
> > personally don't have any computers that don't have support for
> > x86_64-v2 anymore.
> >
> > Does anyone know if anyone is planning to propose this for Fedora
> > anytime soon, either as an addon architecture (like what Arch is
> > doing) or an upgrade of our x86_64 baseline like RHEL is doing?
> >
> > [1]: https://en.opensuse.org/Feature_Planning_15.4
> > [2]: https://developers.redhat.com/blog/2021/01/05/building-red-hat-enterprise-linux-9-for-the-x86-64-v2-microarchitecture-level
> > [3]: https://ml.mageia.org/l/arc/dev/2021-02/msg00583.html
> > [4]: https://www.phoronix.com/scan.php?page=news_item&px=Arch-Linux-x86-64-v3-Port-RFC
>
> Uhmmmm ... you mean something like this?
> https://fedoraproject.org/wiki/Changes/x86-64_micro-architecture_update
> Rejected by FESCo two years ago: https://pagure.io/fesco/issue/2198
>
> If I remember correctly, it was shot down pretty quickly on the devil
> list, because Intel still produced CPUs that do not support AVX2.
> Bumping the baseline to x86_64v2 would be different, since AVX is not
> part of that (but only x86_64v3).
>

Yeah, I think that proposal was not workable because of AVX2. The
x86_64-v2 subarch adds SSSE3, SSE4.2, POPCNT, and CMPXCHG16B to the
current x86_64 baseline. All of these instructions were present in the
first Intel Macs launched in 2007, as I recall.

> Different question: How is the runtime CPU feature detection /
> dispatch support in glibc coming along? Shouldn't this "work" by now?
>

No idea, good question, though!




--
真実はいつも一つ!/ Always, there's only one truth!
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