Re: Fwd: Re: Opinion question (Core2 Duo)

[Jo Shields]

On Wed, 2007-09-19 at 00:08 -0700, Francesco Pietra wrote:
> I have just completed unrestricted MP2/6-31G* energy procedure (after
> DFT/M05-2X) for a 98-atoms (first row) molecule in 19 hours with four-node
> amd64 Debian amd64 etch, NWChem suite. I understand (if I understand 
> correctly)
> from your email that should I have had Core 2 I would not have had the time to
> take a coffee in between launching the MP2 procedure and getting the
> computational results. Interesting.

Xeon/Core2 cheats slightly - it has combined units for both adding and
multiplying on the chip - meaning if you do a multiplication immediately
followed by an addition, then it'll happen in 1 cycle instead of 2,
hence the "twice as many FLOPs" thing. Honestly, in desktop
applications, it doesn't matter much - but in matrix operations, as used
by most chemistry packages such as Gaussian or NWChem, it makes a full
impact.

So yes, you'd probably see a ~90% speed boost moving from an AMD64 to a
Core2 of identical clock speed.

If you have access to the NWChem source (you might not, I don't think we
have any login credentials lying around to check with) you would see
even bigger improvements with a commercial compiler and math library -
you may find a cheaper option to improve performance than buying a new
Core2 rig is to buy Portland C (or Pathscale C), and link against the
free AMD Core Math Library instead of conventional open-source
BLAS/LAPACK routines.

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/ Jo Shields <[EMAIL PROTECTED]> \
| Systems Manager,  |
\ Oxford Supercomputing Centre  /
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Fwd: Re: Opinion question (Core2 Duo)

[Francesco Pietra]

I have just completed unrestricted MP2/6-31G* energy procedure (after
DFT/M05-2X) for a 98-atoms (first row) molecule in 19 hours with four-node
amd64 Debian amd64 etch, NWChem suite. I understand (if I understand correctly)
from your email that should I have had Core 2 I would not have had the time to
take a coffee in between launching the MP2 procedure and getting the
computational results. Interesting.

Thanks

francesco pietra

> --- Jo Shields <[EMAIL PROTECTED]> wrote:
> 
> > Subject: Re: Opinion question (Core2 Duo)
> > From: Jo Shields <[EMAIL PROTECTED]>
> > To: debian-amd64 
> > Date: Tue, 18 Sep 2007 15:51:34 +0100
> > 
> > 
> > On Tue, 2007-09-18 at 10:41 -0400, Lennart Sorensen wrote:
> > > On Tue, Sep 18, 2007 at 03:08:48PM +0100, Jo Shields wrote:
> > > > Or more? Buy an Altix! ;)
> > > 
> > > Ehm, well the Altix uses either the itanium (why would anyone want that
> > > crap) or a dual socket core 2 based cpu.  That hardly matches a 4 or
> > > more cpu opteron server.
> > 
> > Let's assume I have large examples of both IA64 and AMD64. Plus further
> > benchmark data we collected ourselves.
> > 
> > IA64 is fast, for floating point code. On paper, it offers the same
> > per-core-per-Hz FLOP count as Core (twice that of AMD64). And in
> > practise, Altix scales, whilst the competition, well, doesn't. In our
> > benchmarks, IA64 was not only faster per-GHz than POWER5 or AMD64, but
> > faster in absolute terms too, with an 8-way test absolutely dominated by
> > a 1.6-GHz-Montecito-based Altix, whilst AMD64 didn't even register a
> > pulse.
> > 
> > However, for IA64, compiler choice is key - using GCC to compile test
> > code isn't just crippling the system, it's throwing away hundreds of
> > thousands (if not more) of investment
> > 
> > > SGI has nothing of any real interest.  No wonder they went under not
> > > that long ago. :)
> > 
> > They've got SMP machines that don't choke at >4 cores. For some
> > applications, that's of great interest.
> > 
> > -- 
> >  __
> > / Jo Shields <[EMAIL PROTECTED]> \
> > | Systems Manager,  |
> > \ Oxford Supercomputing Centre  /
> >  ---
> >\   ,__,
> > \  (oo)___
> >(__))\
> >   ||--|| *
> > 
> > 
> > -- 
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> > 
> 
> 
> 
>  
>

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