Re: [asa] NASA - Climate Simulation Computer Becomes More Powerful

I realise this is going a bit off the topic of science/faith and more
towards geek-talk, but for climate simulation, would not a more
appropriate benchmark be the performance on SPARSE systems of matrices
rather than dense matrices as in linpack. I'm thinking of schemes of
equations on a finite difference grid, where the connectivity is
between neighbouring grid points etc.

Sparse systems cannot match the floating point performance of dense
systems because of the necessity of indirection (you need one
instruction to fetch the memory location where the (i,j) value is
stored and one to actually fetch the value). In dense matrices the
values are all contiguous in memory and hence can go much faster.

As an aside I use the Intel Math Kernel library and Vector Math
Library extensively in my work.

Iain

On Thu, Sep 10, 2009 at 4:56 PM, Randy Isaac <randyisaac@comcast.net> wrote:
> Dave,
>  It's a Linpack performance benchmark. More details at
> http://www.top500.org/project/linpack So it is a representative performance
> of a dense system of linear equtions. They also give a theoretical peak
> performance but the Linpack measurements is the main criterion.
>
> Randy
>
>
>>>
>> What exactly do these numbers represent?  Are they the peak number of fp
>> ops per second if all goes just exactly right eg no cache misses... you know
>> the drill?  Are they an expected peak number of fp ops/sec under some
>> reasonable assumptions?  Lastly does anyone actually measure the number of
>> fp ops/sec that the application programs actually obtain?
>>
>> I thought Rich's report that the Intel gaming vector floating point
>> instructions were being used for climate modeling was interesting.  Years
>> ago when I was looking at the IA32 instructions I wondered if using these
>> vector instructions might pay off for numerical computation.
>>
>> Dave W
>>
>
>
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