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>, Nathan Bossart <nathandbossart@gmail.com>

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

Date: 2025-02-18T18:27:57Z

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

Hi John, 

Just a few comments on v7: 

> pg_cpucap_crc32c

I like the idea of moving all CPU runtime detection to a single module outside of implementations. This makes it easy to extend in the future and keeps the functionalities separate. 

> - Rename the CRC choose*.c files to pg_cpucap_{x86,arm}.c and build them
> unconditionally for each platform

+1. Sounds perfect. We should also move the avx512 runtime detection of popcount here. The runtime detection code could also be appended with function __attribute__((constructor)) so that it gets executed before main. 

> I think the runtime dispatch is fairly simple for this case.
+ pg_comp_crc32c_sse42(pg_crc32c crc, const void *data, size_t len)
+ {
+ ....
+ #ifdef HAVE_PCLMUL_RUNTIME
+   if (len >= PCLMUL_THRESHOLD && (pg_cpucap & PGCPUCAP_CLMUL))

IMO, the pclmul and sse4.2 versions should be dispatched independently and the dispatch logic should be moved out of the pg_crc32c.h to it own pg_crc32c_dispatch.c file. 

Also, thank you for taking lead on developing this patch. Since the latest patch seems to be in a good shape, I'm happy to provide feedback and review your work, or can continue development work based on any feedback. Please let me know which you'd prefer.

Raghuveer