[Beowulf] Virginia Tech upgrade

Jeff Layton jeffrey.b.layton at lmco.com
Thu Jan 29 11:04:28 EST 2004


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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