[Beowulf] Better C2D or Quadcore

Matthew Knepley knepley at gmail.com
Tue Nov 27 09:26:26 EST 2007


On Nov 27, 2007 8:18 AM, Bill Broadley <bill at cse.ucdavis.edu> wrote:
> >    - high per-CPU memory performance. Each CPU (core in dual core
> >    systems) needs to have its own memory bandwith of roughly 2 or more
> >    gigabytes.
>
> Er, presumably thats 2 or more GB/sec.
>
> > For example, standard dual processor "PC's" will
> > notprovide better performance when the second processor is used, that
>
> Er, standard dual processor PCs can hit 4GB/sec.  Even my $750 desktop from
> dell, lousy memory, 1.8 GHz cpu gets 4GB/sec at stream add and triad:
> Function      Rate (MB/s)   Avg time     Min time     Max time
> Add:         3945.7460       0.0124       0.0122       0.0126
> Triad:       3951.5930       0.0124       0.0121       0.0129

FAQ can't always have a precise explanation. The issue here is balance.

  Machine          & Peak (MF/s) & Triad (MB/s) & MF/MW & Eq. MF/s \\
  Matt's Laptop    &        1700 &       1122.4 & 12.1  &  93.5 (5.5\%) \\
  Intel Core2 Quad &       38400 &       5312.0 & 57.8  & 442.7 (1.2\%) \\

So, yes the bandwidth goes up, but not at anywhere near the rate to keep a
bandwidth hungry matvec satisfied. The first numbers are for my laptop, and the
second are from the STREAMS site. Obviously those are not good percentages of
peak, so yo ucan really get away with slower, cheaper processors.

   Matt
-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which
their experiments lead.
-- Norbert Wiener
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