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

On Thu, May 20, 2021 at 4:54 PM Thomas Gleixner [off-list ref] wrote:

Thomas,

quoted

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