Horton

Re: Popcount optimization using AVX512

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: "Amonson, Paul D" <paul.d.amonson@intel.com>, 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>
Date: 2024-03-29T16:30:14Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Fix __attribute__((target(...))) usage.

  2. Use __attribute__((target(...))) for AVX-512 support.

  3. Fix code for probing availability of AVX-512.

  4. Optimize visibilitymap_count() with AVX-512 instructions.

  5. Optimize pg_popcount() with AVX-512 instructions.

  6. Inline pg_popcount() for small buffers.

  7. Avoid function call overhead of pg_popcount() in syslogger.c.

  8. Refactor code for setting pg_popcount* function pointers.

  9. Inline pg_popcount{32,64} into pg_popcount().

  10. Remove MSVC scripts

  11. Use ARMv8 CRC instructions where available.

  12. Use Intel SSE 4.2 CRC instructions where available.

Nathan Bossart <nathandbossart@gmail.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.

			regards, tom lane