Re: Cost of XLogInsert CRC calculations

> -----Original Message-----
> From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
> Sent: 27 May 2005 15:00
> To: Mark Cave-Ayland (External)
> Cc: 'Manfred Koizar'; 'Greg Stark'; 'Bruce Momjian';
> pgsql-hackers(at)postgresql(dot)org
> Subject: Re: [HACKERS] Cost of XLogInsert CRC calculations
>
>
> "Mark Cave-Ayland" <m(dot)cave-ayland(at)webbased(dot)co(dot)uk> writes:
> > Opt 32 32a 32b 2x32 64 64a 64b
> > --------------------------------------------------------
> > O1 4.91 4.86 5.43 6.00 11.4 11.39 11.39
> > O2 4.96 4.94 4.69 5.18 15.86 18.75 24.73
> > O3 4.82 4.83 4.64 5.18 15.14 13.77 14.73
>
> Not sure I believe these numbers. Shouldn't 2x32 be about
> twice as slow as just one 32-bit CRC?

Well it surprised me, although Manfred's results with VC6 on /MaxSpeed show
a similar margin. The real killer has to be that I wrote a CRC32 routine in
x86 inline assembler (which in comparison to the gcc-produced version stores
the CRC for each iteration in registers instead of in memory as part of the
current frame) which comes in at 6.5s....

Kind regards,

Mark.

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