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

[Ionut Georgescu <george@physik.tu-cottbus.de>]

Yes, it is a 1.5MB cache CPU.

But it might be more than just cache misses. When running with a 256x256
grid, I am actually using 3 256x257 matrices, which is slightly over
1.5MB.  I just made a comparison with a 32x32 grid and the difference is
the same: alpha 10.294s, zx2000 14.777s . -O3 is only by 0.4s faster
than -O2 in this case.

The variations are within +-0.02s between runs (for the 32x32 case).

Is there a way to test the bandwidth of the cache ? Because I think the
alphas have actually 2MB of L2 cache, not L3.

Thanks,
Ionut


On Fri, Oct 24, 2003 at 04:35:43PM +0100, Matthew Wilcox wrote:
> 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 fftw.org
> > 
> > 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
> http://www.spec.org/cpu2000/results/res2000q3/cpu2000-20000630-00134.asc
> 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
> 

-- 
***************
* Ionut Georgescu
* http://www.physik.tu-cottbus.de/~george/
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* "In Windows you can do everything Microsoft wants you to do; in Unix you
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