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Technology Stocks : Advanced Micro Devices - Moderated (AMD)
AMD 207.67+2.2%Jan 12 3:59 PM EST
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To: Dan3 who wrote (240073)9/9/2007 6:24:36 PM
From: graphicsguruRead Replies (1) of 275872
 
SPEC_FP is a suite of real floating point applications put together by Intel engineers

Where do you get the idea that Spec_fp was put together by
Intel? Intel may control Bapco, but not Spec.

Have you taken a look at the benchmark closely? It mostly
consists of fp benchmarks with problem sizes too large to
fit into any existing processor cache. Since fp ops are
super cheap compared with even streaming memory access,
it ends up testing memory bandwidth mainly.

Try it for yourself. Write a program that does a huge
dot product (too big to fit in cache). Run it on
machines with different clock speeds. Not much difference.
Now change the memory timings. Big difference.
Spec_fp is full of problems whose performance characteristics
are like this. That's what Linpack does in its inner loop.
It's representative of a class of problems -- but by no
means all that use fp. Doing lots of small ffts, for
example, is fundamentally different because you mostly get
cache hits, and as a result, video encoding has very
different performance characteristics.

In the good old days, fp ops were *very* expensive compared
to integer ops. Now they're not. It's very important
to keep that in mind. When cache misses cost the same
as hundreds of multiplies, talking about fp performance
takes on a very different meaning from what it used to have.
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