Re: Popcount optimization using AVX512

Nathan Bossart <nathandbossart@gmail.com>

From: Nathan Bossart <nathandbossart@gmail.com>

To: "Amonson, Paul D" <paul.d.amonson@intel.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>

Date: 2024-03-29T16:22:11Z

Lists: pgsql-hackers

Commits

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Fix __attribute__((target(...))) usage.
- 41b98ddb77bf 18.0 landed
Use __attribute__((target(...))) for AVX-512 support.
- f78667bd910e 18.0 landed
Fix code for probing availability of AVX-512.
- 598e0114a3b1 17.0 landed
Optimize visibilitymap_count() with AVX-512 instructions.
- 41c51f0c68b2 17.0 landed
Optimize pg_popcount() with AVX-512 instructions.
- 792752af4eb5 17.0 landed
Inline pg_popcount() for small buffers.
- deb1486c7d36 17.0 landed
Avoid function call overhead of pg_popcount() in syslogger.c.
- 4133c1f45c54 17.0 landed
Refactor code for setting pg_popcount* function pointers.
- 6687430c98f3 17.0 landed
Inline pg_popcount{32,64} into pg_popcount().
- cc4826dd5e52 17.0 landed
Remove MSVC scripts
- 1301c80b2167 17.0 cited
Use ARMv8 CRC instructions where available.
- f044d71e331d 11.0 cited
Use Intel SSE 4.2 CRC instructions where available.
- 3dc2d62d0486 9.5.0 cited

On Fri, Mar 29, 2024 at 10:59:40AM -0500, Nathan Bossart wrote:
> It might be nice if we conditionally built pg_popcount_avx512.o in autoconf
> builds, too, but AFAICT we still need to wrap most of that code with
> macros, so I'm not sure it's worth the trouble.  I'll take another look at
> this...

If we assumed that TRY_POPCNT_FAST would be set and either
HAVE__GET_CPUID_COUNT or HAVE__CPUIDEX would be set whenever
USE_AVX512_POPCNT_WITH_RUNTIME_CHECK is set, we could probably remove the
surrounding macros and just compile pg_popcount_avx512.c conditionally
based on USE_AVX512_POPCNT_WITH_RUNTIME_CHECK.  However, the surrounding
code seems to be pretty cautious about these assumptions (e.g., the CPUID
macros are checked before setting TRY_POPCNT_FAST), so this would stray
from the nearby precedent a bit.

A counterexample is the CRC32C code.  AFAICT we assume the presence of
CPUID in that code (and #error otherwise).  I imagine its probably safe to
assume the compiler understands CPUID if it understands AVX512 intrinsics,
but that is still mostly a guess.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com