[lug] Various Arch/Compiler Binaries living together

[Nate Duehr]

Wow.  Thanks for posting this info Ed.  Quite enlightening.

Nate, nate at natetech.com

On Wed, 2002-06-26 at 12:15, Ed Hill wrote:
> On Wed, 2002-06-26 at 11:52, John Karns wrote:
> >
> > Results are very surprising:
> > 
> > PIII/850:
> > 26.160u 0.000s 0:26.08 100.3%   0+0k 0+0io 115pf+0w
> > Xeon/1.7:
> > 24.300u 0.000s 0:24.30 100.0%   0+0k 0+0io 114pf+0w
> > 
> > Does it make any sense? Both CPUs have the same size cache (256kB)  CPU
> > clock is two times faster on Xeon. The memory is four times faster on Xeon
> > (400MHz RAMBUS vs. 100MHz bus in PIII). So what could be the possible
> > reason for such strange results. I can't imagine that Xeon's floating
> > point operations take twice as many clock ticks to complete as on PIII
> 
> 
> Thanks for posting that!
> 
> If you care about floating point and have been following the information
> on sites like spec.org, aceshardware.com, and tomshardware.com you
> wouldn't be so surprised.  The P4 has *rotten* legacy x87 support.  The
> only way you get good floating point is by having a compiler that can
> generate the SIMD (MMX/SSE/SSE2) instructions.  And gcc, AFAIK, has
> pretty poor support in that area.  So what you're measuring is the
> ability of the chips to execute x87 code.
> 
> Heres a sample from a couple of my machines:
> 
>   PIII/900 (ThinkPad A22p):
>   34.580u 0.020s 0:34.60 100.0%   0+0k 0+0io 112pf+0w
> 
>   Athlon "XP 1700+" (1.5 GHz)
>   17.660u 0.020s 0:17.76 99.5%    0+0k 0+0io 112pf+0w
> 
> Notice how the Athlons *really* shine on x87 code.  They have more x87
> add/multiply pipelines and they totally trash the P4s.
> 
> 
> > On other, not-so-stupid applications, the Xeon performs roughly 1.7-2
> > times faster than PIII. Still, I'm very curious why is it so bad on this
> > simple program.
> 
> Yeah, thats integer performance.  The P4 does have pretty good integer
> performance in some areas.
> 
> Ed
> 
> 
> -- 
> Edward H. Hill III, PhD 
> Post-Doctoral Researcher   |  Emails:      ed at eh3.com, ehill at mines.edu
> Division of ESE            |  URL:         http://www.eh3.com
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-- 
Nate Duehr, nate at natetech.com