Linus Torvalds (torvalds.delete@this.linux-foundation.org) on July 11, 2020 8:34 pm wrote:
> Geoff Langdale (geoff.langdale.delete@this.gmail.com) on July 11, 2020 7:49 pm wrote:
> >
> > But we have some SIMD-based table lookup
> > stuff that's way faster than the integer equivalent both
> > because you're doing a lot of stuff at once, but you're
> > also doing stuff where there's no integer equivalent (there's no PSHUFB for a GPR register).
>
> Yeah, and we might even use some of it. We have places where we do "vectorization" by hand and use integer registers
> to hold as many bytes as possible, and look for '/' or the terminating NUL byte (obviously I'm talking about
> filename copies) and create a hash of the result at the same time, one (integer) word at a time.
>
> We could possibly even have an AVX512 version.
>
> If it was available, and if it didn't tank performance due to frequency issues.
>
> But it isn't, and it does.
>
> Fragmentation kills your market. The fact is, AVX512 isn't worth it, because it's not reliably enough there.
> And I don't think it's reasonably ever going to be, because it was never designed to work on low end.
>
> With a new not-even-released-yet CPU's not supporting it being a case in point.
>
> And that makes AVX512 actively bad. It was literally designed not to be used
> in any generic code, and is basically only useful for "hey, we have this kernel
> of code that is so hot that we'll just create five different versions of it.
>
> What part of that is hard to understand? It sure seems to be something Intel cannot
> get its head around, since Intel keeps making that mistake over and over again.

To Intel it is not a mistake.
Intel’s advertising dollars dictate what benchmarks are run, and those benchmarks will show that the new $1,000 CPU is 30% faster than the old CPU and AMD, and Intel hopes that will drive sales.

Intel does not care about users or developers, it cares about sales and rigged benchmarks.
Bunny commercials and car commercial drive the experience bull.

Without fake benchmarks and advertising dollars everyone would be buying AMD chips as they are better overall at less cost. Intel does NOT want to compete on a level playing field.

AVX 1024 is coming, and will come slowly in multiple incompatible steps.