[lug] Various Arch/Compiler Binaries living together

[Ed Hill]

On Thu, 2002-06-27 at 13:33, Sean Reifschneider wrote:
> On Wed, Jun 26, 2002 at 12:15:50PM -0600, Ed Hill wrote:
> >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
> 
> Intel CPUs have *ALWAYS* had pretty crappy floating-point.  Back in around
> 1995 I did some comparisons between a 60MHz HPPA machine (712/60) and a
> Pentium 100MHz.  My tests were running a raytracer in integer and floating
> point modes on both machines.
> 
> In integer mode, the HP machine was about 3x slower than the PC.  However
> when running the same test using floating point on both machines, the HP
> was easily able to keep up with the PC.  Remember, the HP is a RISC CPU, so
> it's not suprising that 60MHz would be around 3x slower than the 100MHz
> Pentium.
> 
> At the time, the Pentium was a state of the art box, and the HP was around
> 2 years old.  At the time of purchase, the HP was a step down from the top
> end machine (which had an 80MHz CPU).


Hi Sean,

Hey, you're giving me flash-backs!  During that same time-frame, I had a
715/50 and, later, a 715/80 on my desk.  ;-)

You're absolutely right that the Intel chips have traditionally had much
worse floating point than any contemporary RISC CPU.  But in my last
post, I was mainly referring to x87 (or "floating point on x86")
performance.  Intel's only real competition there has been AMD whose K5
and K6 cpus were always inferior on floating point ops and competitive
on integer ops.  But now the situation has changed!  The P4 has lousy
x87 performance and only does well with highly tuned SIMD applications
that generally *require* use of Intel's compiler suite (that is, forget
GCC!) and/or hand-tuning.  The current Athlons (K7) and upcoming
Opterons (K8) do *quite* well on floating point without the SIMD junk,
expensive compilers, and/or tuning gymnastics.

Ok, so this may seem like a silly distinction, but its important if
you're buying workstations for scientific and engineering computation. 
Obviously, the Athlons are a *much* better deal, especially when coupled
with Linux and the GNU toolchain...

Ed

-- 
Edward H. Hill III, PhD 
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