RE: Improve CRC32C performance on SSE4.2

Devulapalli, Raghuveer <raghuveer.devulapalli@intel.com>

From: "Devulapalli, Raghuveer" <raghuveer.devulapalli@intel.com>

To: John Naylor <johncnaylorls@gmail.com>

Cc: Nathan Bossart <nathandbossart@gmail.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, "Shankaran, Akash" <akash.shankaran@intel.com>

Date: 2025-02-24T20:16:28Z

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 →

Include _mm512_zextsi128_si512() in AVX-512 configure probes.
- ccd5bc93fdfe 18.0 landed
Properly fix AVX-512 CRC calculation bug
- 43da394304fb 18.0 landed
Workaround code generation bug in clang
- f83f14881c7a 18.0 landed
Compute CRC32C using AVX-512 instructions where available
- 3c6e8c123896 18.0 landed
Inline CRC computation for small fixed-length input on x86
- e2809e3a1015 18.0 landed
Be more paranoid in configure's checks for CRC and POPCNT intrinsics.
- fdb5dd6331e3 18.0 cited

> Here's another idea to make it more automatic: Give up on initializing every
> capability at once. 

I'm not sure I like giving up this. Initializing and running CPUID check with the attribute constructor is very valuable for two reasons: (1) you get everything done at load time before main and (2) you don’t have to run cpuid check for every feature (popcount, crc32c, or anything else you add in the future) multiple times. It keep the cpuid functionality in a central place that makes it a modular design. 

On MSVC, we could have the first SIMD feature call pg_cpucap_initialize() which runs CPUID stores the cpu features. Any subsequent call can skip (because it has already been initialized) by using a static variable or some other approach. Does this make sense? 

Raghuveer