Horton

Re: Improve CRC32C performance on SSE4.2

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: "Devulapalli, Raghuveer" <raghuveer.devulapalli@intel.com>
Cc: John Naylor <johncnaylorls@gmail.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, "Shankaran, Akash" <akash.shankaran@intel.com>
Date: 2025-02-12T21:18:06Z
Lists: pgsql-hackers

Commits

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  1. Include _mm512_zextsi128_si512() in AVX-512 configure probes.

  2. Properly fix AVX-512 CRC calculation bug

  3. Workaround code generation bug in clang

  4. Compute CRC32C using AVX-512 instructions where available

  5. Inline CRC computation for small fixed-length input on x86

  6. Be more paranoid in configure's checks for CRC and POPCNT intrinsics.

On Wed, Feb 12, 2025 at 09:02:27PM +0000, Devulapalli, Raghuveer wrote:
> Also, do we really need to have both USE_SSE42_CRC32C and USE_SSE42_CRC32C_WITH_RUNTIME_CHECK
> features support? The former macro is used to enable running the SSE42 version without a runtime check 
> when someone builds with -msse4.2. The code looks fine now, but the runtime dispatch rules get complicated
> as we add the PCLMUL and AVX512 dispatch in the future. IMO, this additional complexity is not worth it.
> The cpuid runtime dispatch runs just once when postgres server is first setup and would hardly affect performance. 
> Let me know what you think.

I think the idea behind USE_SSE42_CRC32C is to avoid the function pointer
overhead if possible.  I looked at switching to always using runtime checks
for this stuff, and we concluded that we'd better not [0].

[0] https://postgr.es/m/flat/20231030161706.GA3011%40nathanxps13

-- 
nathan