[R] Xeon CPU and ATLAS

[Prof Brian Ripley]

On 13 Mar 2004, Peter Dalgaard wrote:

> rossini at blindglobe.net (A.J. Rossini) writes:
> 
> > > I think the difference between P4 and Xeon is the SSE1 vs SSE2 thing,
> > > so you'd want the P4SSE2 DLL, but others may be able to speak more
> > > authoritatively. 
> > 
> > SSE1 vs SSE2  is PIII vs PIV (so depends if your xeons are p3 or p4 (?
> > not sure if there is such a thing) based.
> 
> Sure? I have
> 
> turmalin:/usr/local/src/ATLAS/>ls  CONFIG/ARCHS/
> 21164.tgz         ConfDump.log   Makefile    PIIISSE1.tgz    PPCG4AltiVec.tgz
> 21164GOTO.tgz     CreateDef.sh   P4SSE1.tgz  POWER.tgz       PPRO.tgz
> 21264.tgz         CreateDirs.sh  P4SSE2      POWER2Thin.tgz  SGIIP28.tgz
> 21264GOTO.tgz     CreateTar.sh   P4SSE2.tgz  POWER3.tgz      SGIIP30.tgz
> ATHLON.tgz        HP9735.tgz     P5MMX.tgz   PPC604.tgz      SunUS2.tgz
> ATHLON3DNow2.tgz  IA64Itan.tgz   PII.tgz     PPC604e.tgz     SunUS5.tgz
> ATHLONSSE1.tgz    KillDirs.sh    PIII.tgz    PPCG4.tgz       negflt.c
> 
> so it would seem that there's both P4SSE1 and PIIISSE1. However,

That's because ATLAS did not always support SSE2, and it might be
faster not to use it on some systems.

>From Intel's Xeon FAQ
http://www.intel.com/cd/ids/developer/asmo-na/eng/19250.htm

   We had XMM on Pentium® III. What is the difference on Intel Xeon?

   Intel Xeon offers SSE2 technology. In addition to the features of SSE, 
   SSE2 provides support for additional simultaneous 128-bit integer and 
   double-precision floating point calculations.

which seems the definitive answer re Xeons.  (I am 99% sure all P4s have 
the same instructions set which includes SSE2.  The main Xeon differences 
are that multi-processor systems are allowed and the caches are usually 
larger than contemporaneous P4s.)

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595