Horton

Re: Popcount optimization using AVX512

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Nathan Bossart <nathandbossart@gmail.com>, Ants Aasma <ants.aasma@cybertec.at>, "Amonson, Paul D" <paul.d.amonson@intel.com>, David Rowley <dgrowleyml@gmail.com>, Andres Freund <andres@anarazel.de>, "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: 2024-04-02T17:43:48Z
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.

Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
> On 2024-Apr-02, Nathan Bossart wrote:
>> Another idea I had is to turn pg_popcount() into a macro that just uses the
>> pg_number_of_ones array when called for few bytes:
>> 
>> 	static inline uint64
>> 	pg_popcount_inline(const char *buf, int bytes)
>> 	{
>> 		uint64		popcnt = 0;
>> 
>> 		while (bytes--)
>> 			popcnt += pg_number_of_ones[(unsigned char) *buf++];
>> 
>> 		return popcnt;
>> 	}
>> 
>> 	#define pg_popcount(buf, bytes) \
>> 		((bytes < 64) ? \
>> 		 pg_popcount_inline(buf, bytes) : \
>> 		 pg_popcount_optimized(buf, bytes))
>> 
>> But again, I'm not sure this is really worth it for the current use-cases.

> Eh, that seems simple enough, and then you can forget about that case.

I don't like the double evaluation of the macro argument.  Seems like
you could get the same results more safely with

	static inline uint64
	pg_popcount(const char *buf, int bytes)
	{
		if (bytes < 64)
		{
			uint64		popcnt = 0;

			while (bytes--)
				popcnt += pg_number_of_ones[(unsigned char) *buf++];

			return popcnt;
		}
		return pg_popcount_optimized(buf, bytes);
	}

			regards, tom lane