| From: | "Amonson, Paul D" <paul(dot)d(dot)amonson(at)intel(dot)com> |
|---|---|
| To: | Nathan Bossart <nathandbossart(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, David Rowley <dgrowleyml(at)gmail(dot)com>, "Andres Freund" <andres(at)anarazel(dot)de>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, "Shankaran, Akash" <akash(dot)shankaran(at)intel(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | RE: Popcount optimization using AVX512 |
| Date: | 2024-03-29 16:06:17 |
| Message-ID: | BL1PR11MB5304D039E04286E9DF048473DC3A2@BL1PR11MB5304.namprd11.prod.outlook.com |
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| Lists: | pgsql-hackers |
> -----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.
>
> 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 compilers
> support that instruction, we might need an additional configure check and/or
> CPUID check. It looks like MSVC has had support for the _xgetbv intrinsic 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 for Intel 64 bit HW and 2010 for AMD 64bit HW, maybe you could test for _xgetbv() MSVC built-in. How far back do you need to go?
Thanks,
Paul
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