| From: | "Devulapalli, Raghuveer" <raghuveer(dot)devulapalli(at)intel(dot)com> |
|---|---|
| To: | Nathan Bossart <nathandbossart(at)gmail(dot)com> |
| Cc: | John Naylor <johncnaylorls(at)gmail(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>, "Shankaran, Akash" <akash(dot)shankaran(at)intel(dot)com> |
| Subject: | RE: Improve CRC32C performance on SSE4.2 |
| Date: | 2025-02-12 22:46:59 |
| Message-ID: | PH8PR11MB8286CE7C6E1C631792C79782FBFC2@PH8PR11MB8286.namprd11.prod.outlook.com |
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| Lists: | pgsql-hackers |
> > Sounds good to me. Although, users building with just -msse4.2 will
> > now encounter an an additional pclmul runtime check. That would be a
> > regression unless they update to building with both -msse4.2 and -mpclmul.
>
> My thinking was that building with just -msse4.2 would cause the existing SSE 4.2
> implementation to be used (without the function pointer). That's admittedly a bit
> goofy because they'd miss out on the PCLMUL optimization, but things at least
> don't get any worse for them.
Right. We are only talking about a regression for small potion of people who build
with -msse4.2 and run on Nehalem/VM with pclmul disabled where we will run
the cpuid check for pclmul and still pick the sse4.2 version.
Raghuveer
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