Horton

Re: Popcount optimization using AVX512

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Nathan Bossart <nathandbossart@gmail.com>, "Devulapalli, Raghuveer" <raghuveer.devulapalli@intel.com>, "Shankaran, Akash" <akash.shankaran@intel.com>, Tom Lane <tgl@sss.pgh.pa.us>, David Rowley <dgrowleyml@gmail.com>, Ants Aasma <ants.aasma@cybertec.at>, Alvaro Herrera <alvherre@alvh.no-ip.org>, "Amonson, Paul D" <paul.d.amonson@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: 2024-07-31T01:05:18Z
Lists: pgsql-hackers

Commits

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  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.

On Wed, Jul 31, 2024 at 12:50 PM Andres Freund <andres@anarazel.de> wrote:
> It's one thing for the avx512 path to have that overhead, but it's
> particularly absurd for pg_popcount32/pg_popcount64, where
>
> a) The function call overhead is a larger proportion of the cost.
> b) the instruction is almost universally available, including in the
>    architecture baseline x86-64-v2, which several distros are using as the
>    x86-64 baseline.

FWIW, another recent thread about that:

https://www.postgresql.org/message-id/flat/CA%2BhUKGKS64zJezV9y9mPcB-J0i%2BfLGiv3FAdwSH_3SCaVdrjyQ%40mail.gmail.com