Re: Popcount optimization using AVX512

Nathan Bossart <nathandbossart@gmail.com>

From: Nathan Bossart <nathandbossart@gmail.com>

To: "Amonson, Paul D" <paul.d.amonson@intel.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: 2024-03-29T20:08:28Z

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 Fri, Mar 29, 2024 at 02:13:12PM -0500, Nathan Bossart wrote:
> * If the compiler understands AVX512 intrinsics, we assume that it also
>   knows about the required CPUID and XGETBV intrinsics, and we assume that
>   the conditions for TRY_POPCNT_FAST are true.

Bleh, cfbot's 32-bit build is unhappy with this [0].  It looks like it's
trying to build the AVX512 stuff, but TRY_POPCNT_FAST isn't set.

[19:39:11.306] ../src/port/pg_popcount_avx512.c:39:18: warning: implicit declaration of function ‘pg_popcount_fast’; did you mean ‘pg_popcount’? [-Wimplicit-function-declaration]
[19:39:11.306]    39 |  return popcnt + pg_popcount_fast(buf, bytes);
[19:39:11.306]       |                  ^~~~~~~~~~~~~~~~
[19:39:11.306]       |                  pg_popcount

There's also a complaint about the inline assembly:

[19:39:11.443] ../src/port/pg_popcount_avx512_choose.c:55:1: error: inconsistent operand constraints in an ‘asm’
[19:39:11.443]    55 | __asm__ __volatile__(" xgetbv\n":"=a"(low), "=d"(high):"c"(xcr));
[19:39:11.443]       | ^~~~~~~

I'm looking into this...

> +#if defined(HAVE__GET_CPUID)
> +	__get_cpuid_count(7, 0, &exx[0], &exx[1], &exx[2], &exx[3]);
> +#elif defined(HAVE__CPUID)
> +	__cpuidex(exx, 7, 0);

Is there any reason we can't use __get_cpuid() and __cpuid() here, given
the sub-leaf is 0?

[0] https://cirrus-ci.com/task/5475113447981056

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com