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MathGroup Archive 2000

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Re: Help! Mathematica on my 500MHz outperforms my GHz machine!

  • To: mathgroup at smc.vnet.net
  • Subject: [mg23049] Re: Help! Mathematica on my 500MHz outperforms my GHz machine!
  • From: terryis at my-deja.com
  • Date: Thu, 13 Apr 2000 02:43:32 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Fellow Mathematica Users,

After spending some time investigating the lackluster
performance of my gigahertz Athlon machine I have finally
discovered why it only performs at about the same level
as my 500MHz Pentium III. In short my Athlon is bottle-
necking on the relatively slow 100MHz bus between cache
and main memory (as some of you had suspected).

To start with I ran the various benchmarks suggested
to me. From http://fampm201.tu-graz.ac.at/karl/mma.html I
ran the MMA-Test.nb (for Mathematica 3.0) and got the
following results:

   Version   = Microsoft Windows 3.0 (April 25, 1997)
   Times     =
{0.531,0.591,0.18,0.371,1.91,0.661,0.181,0.28,0.551,0.641,0.47,0.862,0.5
81,0.49,0.461}
   Total Kernel Time = 8.763,  Total Time = 9.
   Benchmark = 11.2

The benchmarks at www.scientificweb.com/sciencee/mathstef2.html could
not be found and the ones at
www.geocities.com/SiliconValley/Lab/2255/bytemark.html worked on one of
my computers but gave a 'numeric sort' error condition on the gigahertz
machine.

The link 205.181.113.18/zdbop/zdbop2.html could not be contacted despite
multiple attempts on different occasions.


Next I split up my simulation and timed each piece individually
on each machine. For each piece my Athlon kicked ass even though
it performed poorly on the whole simulation. Finally I
was able to localize the difference in performance to a
single piece of code that saved intermediate results to
memory. With the code to save intermediate results in,
my Athlon took on average 27 minutes to run 25000
iterations of my simulation compared to 24 minutes on the
Pentium. Without the code to save intermediate results the
Athlon was averaging 1 minute compared to 3 minutes on my
Pentium! My conclusion was that without saving intermediate
results, the sum total of all the parts of my simulation
was able to fit completely in cache and so could run at the
full 200MHz bus speed between cache and CPU. Interestingly
enough the performance of the Pentium also improved
dramatically (from 24 minutes down to an average of 3
minutes!) which to me indicated that the cache hit ratio on
the Pentium was not that high either.

As it turns out, my simulations can be re-written to take
full advantage of this machine. Even if I have to go back
and re-run segments of my simulation to re-capture those
intermediate results that are worth capturing, it's still
worth it for me.

Bottom line: if you are certain that what you are doing
can fit into cache then this could very well be one of
the faster machines for you to run Mathematica on.
Otherwise I'd stick with a Pentium based machine.

Finally check out
www.zdnet.com/pcmag/stories/firstlooks/0,6763,2426421,00.html
for a good article that sums up this machines deficiencies.


Sent via Deja.com http://www.deja.com/
Before you buy.


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