Re: add AVX2 support to simd.h

Nathan Bossart <nathandbossart@gmail.com>

From: Nathan Bossart <nathandbossart@gmail.com>

To: John Naylor <johncnaylorls@gmail.com>

Cc: Ants Aasma <ants@cybertec.at>, pgsql-hackers@postgresql.org

Date: 2024-03-15T19:40:16Z

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 →

Improve style of pg_lfind32().
- 7188a7806d20 17.0 landed
Fix compiler warning for pg_lfind32().
- 1f42337be535 17.0 landed
Micro-optimize pg_lfind32().
- 7644a7340c8a 17.0 landed
Introduce helper SIMD functions for small byte arrays
- 9f225e992bed 17.0 cited
Optimize xid/subxid searches in XidInMVCCSnapshot().
- 37a6e5df3713 16.0 cited

Attachments

v3-0001-pg_lfind32-process-tail-with-SIMD-intructions.patch (text/x-diff)

On Fri, Mar 15, 2024 at 12:41:49PM -0500, Nathan Bossart wrote:
> I've also attached the results of running this benchmark on my machine at
> HEAD, after applying 0001, and after applying both 0001 and 0002.  0001
> appears to work pretty well.  When there is a small "tail," it regresses a
> small amount, but overall, it seems to improve more cases than it harms.
> 0002 does regress searches on smaller arrays quite a bit, since it
> postpones the SIMD optimizations until the arrays are longer.  It might be
> possible to mitigate by using 2 registers when the "tail" is long enough,
> but I have yet to try that.

The attached 0003 is a sketch of what such mitigation might look like.  It
appears to help with the regressions nicely.  I omitted the benchmarking
patch in v3 to appease cfbot.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com