| From: | Nathan Bossart <nathandbossart(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | "Amonson, Paul D" <paul(dot)d(dot)amonson(at)intel(dot)com>, 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 16:41:53 |
| Message-ID: | 20240329164153.GC1106154@nathanxps13 |
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| Lists: | pgsql-hackers |
On Fri, Mar 29, 2024 at 12:30:14PM -0400, Tom Lane wrote:
> Nathan Bossart <nathandbossart(at)gmail(dot)com> writes:
>>> 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?
>
>> Hm. It seems unlikely that a compiler would understand AVX512 intrinsics
>> and not XGETBV then. I guess the other question is whether CPUID
>> indicating AVX512 is enabled implies the availability of XGETBV on the CPU.
>> If that's not safe, we might need to add another CPUID test.
>
> Some quick googling says that (1) XGETBV predates AVX and (2) if you
> are worried about old CPUs, you should check CPUID to verify whether
> XGETBV exists before trying to use it. I did not look for the
> bit-level details on how to do that.
That extra CPUID check should translate to exactly one additional line of
code, so I think I'm inclined to just add it.
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
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