Re: Opinion question (Core2 Duo)
On Tue, 2007-09-18 at 18:29 -0400, Douglas A. Tutty wrote:
> On Tue, Sep 18, 2007 at 11:16:14AM -0400, Lennart Sorensen wrote:
>
> > Well if you need something to do floating point, then x86 isn't
> > generally where you want to be. And yes if performance matters gcc
> is
> > not what you want to use either.
> >
>
> Is there a free alternative to GCC?
Free? None worth using. Gratis? ICC, but only if you're unemployed.
Look at it this way though. On a 64-node cluster, you'd be paying an
extra £80 per machine (i.e. £5120) for a single chip-speed bump of about
16%. You'd pay an order of magnitude less for a decent compiler, which
will get significantly better performance increases than the cpu speed
bump.
Nobody likes proprietary software (especially us sysadmins who need to
make it work) but it's basic economics - 16% for £5k or 100% for £0.5k
> Where would you go for floating point? Last time I looked, Cray used
> Opterons as nodes in its supercomputers.
Once you go beyond the desktop, a major factor becomes scalability, and
ease of programming. Best bang-per-buck performance comes from a cluster
of dual-dual-core Xeon nodes, with a reasonable message-passing
interface like Infiniband. However, MPI programming is awkward (and in
some problems sets not possible). In the land of SMP or Vector, you look
at application scalability - if a 16-core Opteron system like a Tyan
VX50 shows 0% improvement moving from 8 to 16 cores with a quantum
chemistry code, and an Altix shows ~95% improvement, it's a no-brainer
as to which is the better system to pick for that code.
So for *small* codes, Xeon is a floating point monster. If you want
scalable, you need to run a few benchmarks and decide what's an
important factor for you (is your code parallel enough that a 8, 16, 32
or even 128 core limit per machine is a problem?).
Then look at cost, choke on your coffee, and go back to buying Xeon
clusters
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/ Jo Shields <jms@osc.ox.ac.uk> \
| Systems Manager, |
\ Oxford Supercomputing Centre /
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