| From: | Nathan Bossart <nathandbossart(at)gmail(dot)com> |
|---|---|
| To: | "Devulapalli, Raghuveer" <raghuveer(dot)devulapalli(at)intel(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 21:18:06 |
| Message-ID: | Z60QDnEuYptMjbQO@nathan |
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| Lists: | pgsql-hackers |
On Wed, Feb 12, 2025 at 09:02:27PM +0000, Devulapalli, Raghuveer wrote:
> Also, do we really need to have both USE_SSE42_CRC32C and USE_SSE42_CRC32C_WITH_RUNTIME_CHECK
> features support? The former macro is used to enable running the SSE42 version without a runtime check
> when someone builds with -msse4.2. The code looks fine now, but the runtime dispatch rules get complicated
> as we add the PCLMUL and AVX512 dispatch in the future. IMO, this additional complexity is not worth it.
> The cpuid runtime dispatch runs just once when postgres server is first setup and would hardly affect performance.
> Let me know what you think.
I think the idea behind USE_SSE42_CRC32C is to avoid the function pointer
overhead if possible. I looked at switching to always using runtime checks
for this stuff, and we concluded that we'd better not [0].
[0] https://postgr.es/m/flat/20231030161706.GA3011%40nathanxps13
--
nathan
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