Horton

Re: Improve CRC32C performance on SSE4.2

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: John Naylor <johncnaylorls@gmail.com>
Cc: "Devulapalli, Raghuveer" <raghuveer.devulapalli@intel.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, "Shankaran, Akash" <akash.shankaran@intel.com>
Date: 2025-03-05T15:52:22Z
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 →

  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, Mar 05, 2025 at 08:51:21AM +0700, John Naylor wrote:
> That was my hunch too, but I wanted to be more sure, so I modified the
> benchmark so it doesn't know the address of the next calculation until
> it finishes the last calculation so we can hopefully see the latency
> caused by indirection. It also does an additional calculation on
> constant 20 bytes, like the WAL header. I also tweaked the length each
> iteration so the branch predictor maybe has a harder time predicting
> the constant 20 input. And to make it more challenging, I removed the
> part that inlined all small inputs, so it inlines only constant
> inputs:

Would you mind sharing this test?  It sounds like you are running a
workload with a mix of constant/inlined calls and function pointer calls to
simulate typical usage for WAL, but I'm not 100% sure I'm understanding you
correctly.

> These are still a bit noisy, and close, but, it seems there is no
> penalty in using the function pointer as long as the header
> calculation is inlined.

These results look promising.

-- 
nathan