Re: Popcount optimization using AVX512
Alvaro Herrera <alvherre@alvh.no-ip.org>
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: "Amonson, Paul D" <paul.d.amonson@intel.com>, Tom Lane <tgl@sss.pgh.pa.us>, 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: 2024-04-01T11:06:12Z
Lists: pgsql-hackers
Commits
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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-Mar-31, Nathan Bossart wrote:
> +uint64
> +pg_popcount_avx512(const char *buf, int bytes)
> +{
> + uint64 popcnt;
> + __m512i accum = _mm512_setzero_si512();
> +
> + for (; bytes >= sizeof(__m512i); bytes -= sizeof(__m512i))
> + {
> + const __m512i val = _mm512_loadu_si512((const __m512i *) buf);
> + const __m512i cnt = _mm512_popcnt_epi64(val);
> +
> + accum = _mm512_add_epi64(accum, cnt);
> + buf += sizeof(__m512i);
> + }
> +
> + popcnt = _mm512_reduce_add_epi64(accum);
> + return popcnt + pg_popcount_fast(buf, bytes);
> +}
Hmm, doesn't this arrangement cause an extra function call to
pg_popcount_fast to be used here? Given the level of micro-optimization
being used by this code, I would have thought that you'd have tried to
avoid that. (At least, maybe avoid the call if bytes is 0, no?)
--
Álvaro Herrera 48°01'N 7°57'E — https://www.EnterpriseDB.com/
"El Maquinismo fue proscrito so pena de cosquilleo hasta la muerte"
(Ijon Tichy en Viajes, Stanislaw Lem)