Horton

Re: Popcount optimization using AVX512

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: David Rowley <dgrowleyml@gmail.com>
Cc: Ants Aasma <ants.aasma@cybertec.at>, Alvaro Herrera <alvherre@alvh.no-ip.org>, "Amonson, Paul D" <paul.d.amonson@intel.com>, Tom Lane <tgl@sss.pgh.pa.us>, 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: 2024-04-06T19:41:01Z
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.

Attachments

On Sat, Apr 06, 2024 at 02:51:39PM +1300, David Rowley wrote:
> On Sat, 6 Apr 2024 at 14:17, Nathan Bossart <nathandbossart@gmail.com> wrote:
>> On Sat, Apr 06, 2024 at 12:08:14PM +1300, David Rowley wrote:
>> > Won't Valgrind complain about this?
>> >
>> > +pg_popcount_avx512(const char *buf, int bytes)
>> >
>> > + buf = (const char *) TYPEALIGN_DOWN(sizeof(__m512i), buf);
>> >
>> > + val = _mm512_maskz_loadu_epi8(mask, (const __m512i *) buf);
>>
>> I haven't been able to generate any complaints, at least with some simple
>> tests.  But I see your point.  If this did cause such complaints, ISTM we'd
>> just want to add it to the suppression file.  Otherwise, I think we'd have
>> to go back to the non-maskz approach (which I really wanted to avoid
>> because of the weird function overhead juggling) or find another way to do
>> a partial load into an __m512i.
> 
> [1] seems to think it's ok.  If this is true then the following
> shouldn't segfault:
> 
> The following seems to run without any issue and if I change the mask
> to 1 it crashes, as you'd expect.

Cool.

Here is what I have staged for commit, which I intend to do shortly.  At
some point, I'd like to revisit converting TRY_POPCNT_FAST to a
configure-time check and maybe even moving the "fast" and "slow"
implementations to their own files, but since that's mostly for code
neatness and we are rapidly approaching the v17 deadline, I'm content to
leave that for v18.

-- 
Nathan Bossart
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