Re: Itanium2@900MHz slower than alpha@666MHz ?

From: Matthew Wilcox <>
Date: 2003-10-25 01:35:43
On Fri, Oct 24, 2003 at 05:14:50PM +0200, Ionut Georgescu wrote:
> I am puzzled about the speed of a zx2000 workstation with a 900Mhz CPU.
> According to the SPECfp2000 benchmarks, this workstation should be about
> twice as fast as a DS10 alpha workstation and according to the fftw2
> benchmarks at least 50% faster (double precision, real data, 256x256 FFT
> transforms). I ran the fftw2 benchmark myself and I could reproduce the
> data on
> However, my program is about 40% slower on the zx2000 as on the alpha.
> It only does some Fourier transforms (fftw2, 256x256) and some matrix
> operations (sort of an inner product). Both fftw2 and the program have
> been compiled with ecc -O2 -ipo -limf. ecc is Version 7.1, Build
> 20030307.

This strikes me as possibly being a cache size thing.  Do you have the
1.5MB cache or 3MB cache version of the 900MHz Itanium?  The DS10 specs
I found at
say it has a 2MB cache, so if your data set fits in a 2MB cache and not
in a 1.5MB cache, that would be a possible cause.

What kind of fluctuations do you see between runs?  Linux doesn't
do cache-colouring, so high variation between runs could indicate a
close-to-edge-of-cache scenario.

"It's not Hollywood.  War is real, war is primarily not about defeat or
victory, it is about death.  I've seen thousands and thousands of dead bodies.
Do you think I want to have an academic debate on this subject?" -- Robert Fisk
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Received on Fri Oct 24 11:38:24 2003

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