In article <web.3ef882511b6e269c7f877a1c0@news.povray.org> , "hamburg" 
<ham### [at] fasharvardedu> wrote:

> Yeah.  Although if you read the fine print in the veritest pdf, it becomes
> clear that they rather lied about some of that.

I suppose you read that strange page macnn.com pointed to?  That person
there actually didn't really understand SPEC benchmarking at all.  Half of
the conclusions were wrong there because the person did not notice that SPEC
speed tests run always only run on a single processor.  And single processor
systems do outperform multiprocessor systems (using even exactly the same
configuration otherwise) in a single processor benchmark by a few percent
because there is some unavoidable overhead managing multiple CPUs in
hardware.

> If you compare to, say, Dell's
> benchmarks of their own systems (which are probably similarly deceptive),
> Apple's are competitive but not the best.

Actually, the problem is that Apple used gcc on the Macs while IBM always
uses the AIX compiler when publishing SPEC results.  gcc is just plain
terrible compared to any vendor specific compiler tuned for maximum SPEC
benchmark performance.  Intel is kind of king there because, if you actually
look closely at the stats, the Intel compiler does a really almost perfect
job optimising for the SPEC benchmark.  That is why everybody publishing
results for x86 (or IA64) uses the Intel compiler, and not any other.

gcc on the other hand has always even been at least 20% behind code
generated by CodeWarrior for the PowerPC (as well as Power) platform.  In
fact, Apple is constantly working to improve gcc code generated for PowerPC
for exactly this problem.  Another problem is that gcc is one of the slowest
compilers available - CodeWarrior will easily run ten or 20 times faster
compiling the exact same source code (and still generate faster code).

> Apple is releasing a G5-optimizing version of GCC as part of the free
> devtools upgrade (XCode I think it's called).  I don't know how good their
> optimizations are, but they are there.

Apple cannot fix some inherent problems with certain high-level
optimisations in gcc.  It cannot really fix the speed problems the compiler
has itself (only hide them a bit by adding support for precompiled headers,
as they did recently).  In particular, gcc does tend to have a serious
problem with its loop-optimiser being ten years behind even the published
methods for optimising loops (this is something supposedly being addressed
in gcc 3.4 or 3.5).  All Apple can do is to add good instruction scheduling.
However, there is still no DFA scheduler for PowerPC processors yet, which
did some boost of performance of x86 code generated by gcc.

So, in some sense, Apple did use a fair comparison.  However, given that
they don't have any better compiler for Macs, that is indeed their problem.
And a processor as complex as the Power4 or PowerPC 970 simply needs a damn
good compiler.  Intel has really proven that the compiler makes all the
difference when they addressed performance problems of the Pentium 4 due to
its extremely long pipeline (which helps it to rise clock rates though).

    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

Visit POV-Ray on the web: http://mac.povray.org

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