| From: | "Amonson, Paul D" <paul(dot)d(dot)amonson(at)intel(dot)com> |
|---|---|
| To: | Nathan Bossart <nathandbossart(at)gmail(dot)com> |
| Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Andres Freund <andres(at)anarazel(dot)de>, "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: Proposal for Updating CRC32C with AVX-512 Algorithm. |
| Date: | 2024-08-26 19:15:47 |
| Message-ID: | BL1PR11MB53042196148C54E95531C20ADC8B2@BL1PR11MB5304.namprd11.prod.outlook.com |
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| Lists: | pgsql-hackers |
> IMHO that would be useful to establish the current state of the patch set from
> a performance standpoint, especially since you've added code intended to
> mitigate the regression.
Ok.
> +#define COMP_CRC32C_SMALL(crc, data, len) \
> + ((crc) = pg_comp_crc32c_sse42((crc), (data), (len)))
>
> My interpretation of Andres's upthread suggestion is that we'd add the length
> check within the macro instead of introducing a separate one. We'd expect
> the compiler to optimize out comparisons for small lengths known at compile
> time and always call the existing implementation (which may still involve a
> function pointer in most cases).
How does the m4/compiler know the difference between a const "len" and a dynamic "len"? I already when the code and changed constant sizes (structure sizes) to the new macro. Can you give an example of how this could work?
Paul
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