Horton

RE: Popcount optimization using AVX512

Amonson, Paul D <paul.d.amonson@intel.com>

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From: "Amonson, Paul D" <paul.d.amonson@intel.com>
To: Nathan Bossart <nathandbossart@gmail.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: 2024-03-29T16:06:17Z
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.

> -----Original Message-----
>
> Cool.  I think we should run the benchmarks again to be safe, though.

Ok, sure go ahead. :)

> >> I forgot to mention that I also want to understand whether we can
> >> actually assume availability of XGETBV when CPUID says we support
> >> AVX512:
> >
> > You cannot assume as there are edge cases where AVX-512 was found on
> > system one during compile but it's not actually available in a kernel
> > on a second system at runtime despite the CPU actually having the
> > hardware feature.
> 
> Yeah, I understand that much, but I want to know how portable the XGETBV
> instruction is.  Unless I can assume that all x86_64 systems and compilers
> support that instruction, we might need an additional configure check and/or
> CPUID check.  It looks like MSVC has had support for the _xgetbv intrinsic for
> quite a while, but I'm still researching the other cases.

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?

Thanks,
Paul