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From: Tom Lane <[email protected]>
To: Nathan Bossart <[email protected]>
Cc: Jeff Davis <[email protected]>
Cc: [email protected]
Cc: [email protected]
Subject: Re: always use runtime checks for CRC-32C instructions
Date: Tue, 31 Oct 2023 15:42:33 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <20231030161706.GA3011@nathanxps13>
	<[email protected]>
	<[email protected]>
	<20231031033601.GA68409@nathanxps13>
	<20231031155518.GA70172@nathanxps13>
	<[email protected]>

I wrote:
> I did a more thorough scrape of the buildfarm results.  Of 161 animals
> currently reporting configure output on HEAD, we have

Oh ... take "current" with a grain of salt there, because I just noticed
that I typo'd my search condition so that it collected results from all
systems that reported since 2022-Oct, rather than in the last month as
I'd intended.  There are just 137 animals currently reporting.

Of those, I broke down the architectures reporting using slicing-by-8:

# select arch,count(*) from results where crc = 'slicing-by-8' group by 1 order by 1;
        arch        | count 
--------------------+-------
 aarch64            |     1
 macppc             |     1
 mips64eb; -mabi=64 |     1
 mips64el; -mabi=32 |     1
 ppc64 (power7)     |     4
 ppc64 (power8)     |     2
 ppc64le            |     7
 ppc64le (power8)   |     1
 ppc64le (power9)   |    15
 riscv64            |     2
 s390x (z15)        |    14
 sparc              |     1
(12 rows)

The one machine using slicing-by-8 where there might be a better
alternative is arowana, which is CentOS 7 with a pretty ancient gcc
version.  So I reject the idea that slicing-by-8 is an appropriate
baseline for comparisons.  There isn't anybody who will see an
improvement over current behavior: in the population of interest,
just about all platforms are using CRC instructions with or without
a runtime check.

			regards, tom lane

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