Re: Candidate Linux ABI for Intel AMX and hypothetical new related features

[Len Brown]

On Thu, May 20, 2021 at 4:54 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:

Thomas,

> > AMX is analogous to the multiplier used by AVX-512.
> > The architectural state must exist on every CPU, including HT siblings.
> > Today, the HT siblings share the same execution unit,
> > and I have no reason to expect that will change.
>
> I'm well aware that HT siblings share the same execution unit for
> AVX.
>
> Though AMX is if I remember the discussions two years ago correctly
> shared by more than the HT siblings which makes things worse.

I regret that we were unable to get together in the last year to have
an updated discussion.  I think if we had, then we would have saved
a lot of mis-understanding and a lot of email!

So let me emphasize here:

There is one TMUL execution unit per core.
It is shared by the HT siblings within that core.

So the comparison to the AVX-512 multiplier is a good one.

Len Brown, Intel Open Source Technology Center