Horton

Re: Popcount optimization using AVX512

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: "Amonson, Paul D" <paul.d.amonson@intel.com>
Cc: Andres Freund <andres@anarazel.de>, Alvaro Herrera <alvherre@alvh.no-ip.org>, "Shankaran, Akash" <akash.shankaran@intel.com>, Noah Misch <noah@leadboat.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: 2024-03-12T01:34:36Z
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 Mon, Mar 11, 2024 at 09:59:53PM +0000, Amonson, Paul D wrote:
> I will be splitting the request into 2 patches. I am attaching the first
> patch (refactoring only) and I updated the commitfest entry to match this
> patch. I have a question however:
> Do I need to wait for the refactor patch to be merged before I post the
> AVX portion of this feature in this thread?

Thanks.  There's no need to wait to post the AVX portion.  I recommend
using "git format-patch" to construct the patch set for the lists.

>> Apologies for harping on this, but I'm still not seeing the need for these
>> SIZEOF_VOID_P changes.  While it's unlikely that this makes any practical
>> difference, I see no reason to more strictly check SIZEOF_VOID_P here.
> 
> I got rid of the second occurrence as I agree it is not needed but unless
> you see something I don't how to know which function to call between a
> 32-bit and 64-bit architecture? Maybe I am missing something obvious?
> What exactly do you suggest here? I am happy to always call either
> pg_popcount32() or pg_popcount64() with the understanding that it may not
> be optimal, but I do need to know which to use.

I'm recommending that we don't change any of the code in the pg_popcount()
function (which is renamed to pg_popcount_slow() in your v6 patch).  If
pointers are 8 or more bytes, we'll try to process the buffer in 64-bit
chunks.  Else, we'll try to process it in 32-bit chunks.  Any remaining
bytes will be processed one-by-one.

-- 
Nathan Bossart
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