[Nottingham] <OT> Intel specific optimisiation benchmark

[Martin]

David Ginger (by way of David Ginger ) wrote:
> I thought dome of you would enjoy reading this:

The unbroken link is:
http://groups.google.ca/groups?dq=&hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=a13e403a.0402091438.14018f5a%40posting.google.com&rnum=1&prev=/groups%3Fdq%3D%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26group%3Dcomp.arch%26selm%3Da13e403a.0402091438.14018f5a%2540posting.google.com

Interesting detective work... but there can be many sides to a story...


[Intel compiler optimisation tricks compared running on an Intel P4 and 
an AMD FX51]
###
... First I ran the "generic x86" binaries on the FX51, and then
tried to run the "Intel-only" binaries. The Intel-specific ones
printed out an error message saying that the processor was not
supported and exited.  This wasn't very helpful, was it true that only
Intel processors could take advantage of this performance boost?

I started mucking around with a dissassembly of the Intel-specific
binary and found one particular call (proc_init_N) that appeared to be
performing this check. ...

[check removed] ... it was able to run on the FX51. Much to my
surprise, it ran fine and did not miscompare. On top of that, it got
the same 22% performance boost that I saw on the Pentium4 with an
actual Intel processor.

... From the way it looks right now, it appears that Intel
is simply "cheating" to make their processors look better against
competitor's processors.
###

###
... Intel doesn't have that control
over AMD processors, and one of the optimizations might not work on an
AMD, which would make Intel look bad.  Keep in mind, Intel isn't
likely to pass up a chance to make themselves look better than AMD,
but Intel also likes to ensure that their products work as well as
possible, especially after some of the times that they have been
burned.
###


Still a convenient cheat to my mind. Intel /could/ be a little more open 
about what they are doing...

Good stuff,
Martin

-- 
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Martin Lomas
martin at ml1.co.uk
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