[Beowulf] Virginia Tech upgrade

[Jeff Layton]

Don,

   Is there any way you could run two copies of Stream
at the same time, one on each CPU? I'd like to see the
effect of the memory subsystem.

Thanks!

Jeff

>
> With gcc 2.95.3, -O3, I get on a dual 2.0 GHz G5:
>
>
> Total memory required = 183.1 MB, walltime clock
> -------------------------------------------------------------
> Function      Rate (MB/s)   RMS time     Min time     Max time
> Copy:        2848.7459       0.0450       0.0449       0.0457
> Scale:       2851.4134       0.0453       0.0449       0.0457
> Add:         3470.4630       0.0556       0.0553       0.0557
> Triad:       3456.0981       0.0557       0.0556       0.0561
>
> and with the beta IBM compiler (VAC 6.0, -O5):
>
> -------------------------------------------------------------
> Function      Rate (MB/s)   RMS time     Min time     Max time
> Copy:        2923.5762       0.0439       0.0438       0.0441
> Scale:       2566.9303       0.0500       0.0499       0.0502
> Add:         2304.2857       0.0834       0.0833       0.0836
> Triad:       2339.1539       0.0822       0.0821       0.0823
>
>
> The data bus is a bit unconventional, in that it's split - 32 bits
> read-only, 32 bits write-only.  The two halves can run at the same time.
>
> For moving data, that configuration is nicely balanced.  For
> computations, it may not be so well balanced.  For example, most of the
> flops in one of our codes occur doing small complex matrix-vector
> multiplies.  One typical kernel reads 96 single precision operands, and
> writes only 6 single precision results.  The effective memory bandwidth
> for this is much reduced - instead of a 1 GHz FSB, it's more like an
> effective 500 MHz FSB.
>
> Don Holmgren
> Fermilab
>
>
> On Tue, 27 Jan 2004, Mark Hahn wrote:
>
> > I draw several conclusions from the VT cluster:
> >
> >       - HPL is very cache-friendly.  the dual-G5 has an impressive peak
> >       flops rating, but pretty mediocre memory bandwidth.  anyone 
> have a
> >       Stream result for a G5?  I'd guess around 2.5 GB/s.
> >
> <snip>
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-- 
Dr. Jeff Layton
Aerodynamics and CFD
Lockheed-Martin Aeronautical Company - Marietta



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