From: "Amonson, Paul D" <paul.d.amonson@intel.com>
To: Nathan Bossart <nathandbossart@gmail.com>
CC: Tom Lane <tgl@sss.pgh.pa.us>, David Rowley <dgrowleyml@gmail.com>, "Andres
 Freund" <andres@anarazel.de>, Alvaro Herrera <alvherre@alvh.no-ip.org>,
	"Shankaran, Akash" <akash.shankaran@intel.com>, Noah Misch
	<noah@leadboat.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>,
	"pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Subject: RE: Popcount optimization using AVX512
Thread-Topic: Popcount optimization using AVX512
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Date: Fri, 29 Mar 2024 16:06:17 +0000
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Precedence: bulk

> -----Original Message-----
>
> Cool.  I think we should run the benchmarks again to be safe, though.

Ok, sure go ahead. :)

> >> I forgot to mention that I also want to understand whether we can
> >> actually assume availability of XGETBV when CPUID says we support
> >> AVX512:
> >
> > You cannot assume as there are edge cases where AVX-512 was found on
> > system one during compile but it's not actually available in a kernel
> > on a second system at runtime despite the CPU actually having the
> > hardware feature.
>=20
> Yeah, I understand that much, but I want to know how portable the XGETBV
> instruction is.  Unless I can assume that all x86_64 systems and compiler=
s
> support that instruction, we might need an additional configure check and=
/or
> CPUID check.  It looks like MSVC has had support for the _xgetbv intrinsi=
c for
> quite a while, but I'm still researching the other cases.

I see google web references to the xgetbv instruction as far back as 2009 f=
or Intel 64 bit HW and 2010 for AMD 64bit HW, maybe you could test for _xge=
tbv() MSVC built-in. How far back do you need to go?

Thanks,
Paul