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RE: Proposal for Updating CRC32C with AVX-512 Algorithm. - Mailing list pgsql-hackers

From Amonson, Paul D
Subject RE: Proposal for Updating CRC32C with AVX-512 Algorithm.
Date
Msg-id BL1PR11MB530433DCF3F3EC3EFC5A3430DC8B2@BL1PR11MB5304.namprd11.prod.outlook.com
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In response to Re: Proposal for Updating CRC32C with AVX-512 Algorithm.  (Nathan Bossart <nathandbossart@gmail.com>)
Responses Re: Proposal for Updating CRC32C with AVX-512 Algorithm.
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> I'm curious about where exactly the regression is coming from.  Is it possible
> that your build for the SSE 4.2 tests was using it unconditionally, i.e.,
> optimizing away the function pointer?

I am calling the SSE 4.2 implementation directly; I am not even building the pg_sse42_*_choose.c file with the AVX512
choice.As best I can tell there is one extra function call and one extra int64 conditional test when bytes are <256 and
aof course a JMP instruction to skip the AVX512 implementation. 

Paul

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