Re: Popcount optimization using AVX512

Alvaro Herrera <alvherre@alvh.no-ip.org>

From: Alvaro Herrera <alvherre@alvh.no-ip.org>

To: "Shankaran, Akash" <akash.shankaran@intel.com>

Cc: Nathan Bossart <nathandbossart@gmail.com>, Noah Misch <noah@leadboat.com>, "Amonson, Paul D" <paul.d.amonson@intel.com>, Tom Lane <tgl@sss.pgh.pa.us>, Matthias van de Meent <boekewurm+postgres@gmail.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>

Date: 2024-01-26T06:42:33Z

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 →

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 2024-Jan-25, Alvaro Herrera wrote:

> Finally, the matter of using ifunc as proposed by Noah seems to be still
> in the air, with no patches offered for the popcount family.

Oh, I just realized that the patch as currently proposed is placing the
optimized popcount code in the path that does not require going through
a function pointer.  So the performance increase is probably coming from
both avoiding jumping through the pointer as well as from the improved
instruction.

This suggests that finding a way to make the ifunc stuff work (with good
performance) is critical to this work.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"The ability of users to misuse tools is, of course, legendary" (David Steele)
https://postgr.es/m/11b38a96-6ded-4668-b772-40f992132797@pgmasters.net