Hi,

Linus Torvalds (torvalds.delete@this.linux-foundation.org) on May 23, 2022 12:30 pm wrote:
> Brendan (btrotter.delete@this.gmail.com) on May 23, 2022 12:41 am wrote:
> >
> > For some reason you think my "libraries keep doing what they do now (using the
> > common subset when ISA is different)" is completely different to your "libraries
> > keep doing what they do now (using the common subset when ISA is different)"?
>
> No.
>
> I think your "common subset" is pure and utter garbage, and makes AVX512 worthless.
>
> If libraries use the "common subset", then they won't be using
> AVX512 at all by default in a heterogeneous situation.
>
> And if they don't use AVX512 by default, then AVX512 is simply worthless, and shouldn't
> be wasting any silicon that could be much better used for other things.
>
> That's my argument. If 99% of all AVX use is by libraries (and that's simply reality,
> as shown by AVX2), then if the library by default only uses the common subset of
> the ISA, then the "extended subset" is just waste and should be killed.
>
> End result: heterogeneous ISAs don't work outside of embedded environments
> (and the s390 counter-example mentioned in this thread is not really a counter-example:
> s390 is practically speaking about as embedded as you can be).
>
> I'm simply not interested in your "special case code" thing. Special case
> code simply doesn't matter in the big picture. It's mental masturbation.

Mental masturbation is things like circular logic - e.g. "I don't want to support anything except the common case, because the common case is useless, because I didn't want to support anything except the common case".

- Brendan