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

(cut)

> Not sure I believe these numbers. Shouldn't 2x32 be about twice as
> slow as just one 32-bit CRC?

Also I've just quickly tested on the Xeon Linux FC1 box I used with my
original program using Manfred's program and the margin is even closer:

Opt 32 32a 32b 2x32 64 64a 64b
------------------------------------------------------
O1 2.75 2.81 2.71 3.16 3.53 3.64 7.25
O2 2.75 2.78 2.87 2.94 7.63 10.61 11.93
O3 2.84 2.85 3.03 2.99 7.63 7.64 7.71

I don't know whether gcc is just producing an inefficient CRC32 compared to
2x32 but the results seem very odd.... There must be something else we are
missing?

Kind regards,

Mark.

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