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Re: New CRC algorithm: Slicing by 8

From: Mark Kirkwood <markir(at)paradise(dot)net(dot)nz>
To: PGSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, mark(at)mark(dot)mielke(dot)cc, Gurjeet Singh <singh(dot)gurjeet(at)gmail(dot)com>
Subject: Re: New CRC algorithm: Slicing by 8
Date: 2006-10-23 10:26:34
Message-ID: 453C98DA.7040805@paradise.net.nz (view raw or flat)
Thread:
Lists: pgsql-hackers
Mark Kirkwood wrote:
> Tom Lane wrote:

>> Are you running similar gcc versions on both?  I realize I forgot to
>> document what I was using:

> Ah - good point, FreeBSD is using an older compiler:
> 
> FreeBSD: gcc (GCC) 3.4.6 [FreeBSD] 20060305
> Linux: gcc (GCC) 4.1.1 (Gentoo 4.1.1)
> 
> Hmm - there is a FreeBSD port for 4.1.2, I might set that off to build 
> itself and see if compiling with it changes the results any....
>

Here are the results after building gcc 4.1.2 (repeating results for gcc 
3.4.6 for comparison). I suspect that performance is probably impacted 
because gcc 4.1.2 (and also the rest of the tool-chain) is built with 
gcc 3.4.6 - but it certainly suggests that the newer gcc versions don't 
  like the slice-8 algorithm for some reason.

             Std crc     Slice-8 crc

Intel P-III 1.26Ghz (FreeBSD 6.2 gcc 3.4.6)

8192 bytes  12.975314   14.503810
1024 bytes  1.633557    1.852322
64 bytes    0.111580    0.206975

Intel P-III 1.26Ghz (FreeBSD 6.2 gcc 4.1.2)

8192 bytes  19.516974   29.457739
1024 bytes  2.448570    3.742106
64 bytes    0.112644    0.335292

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Subject: Re: New CRC algorithm: Slicing by 8
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