[Beowulf] scalability

Chris Samuel csamuel at vpac.org
Thu Dec 10 16:33:46 PST 2009

----- "Gus Correa" <gus at ldeo.columbia.edu> wrote:

> This is about the same number I've got for an atmospheric model
> in a dual-socket dual-core Xeon computer.
> Somehow the memory path/bus on these systems is not very efficient,
> and saturates when more than two processes do
> intensive work concurrently.
> A similar computer configuration with dual- dual-
> AMD Opterons performed significantly better on the same atmospheric
> code (efficiency close to 90%).

The issue is that there are Xeon's and then there
are Xeon's.

The older Woodcrest/Clovertown type CPUs had the
standard Intel bottleneck of a single memory
controller for both sockets.

The newer Nehalem Xeon's have HyperTransport^W QPI
which involves each socket having its own memory
controller with connections to local RAM.

This is essentially what AMD have been doing with
Opteron for years and why they've traditionally
done better than Intel with memory intensive codes.

Christopher Samuel - (03) 9925 4751 - Systems Manager
 The Victorian Partnership for Advanced Computing
 P.O. Box 201, Carlton South, VIC 3053, Australia
VPAC is a not-for-profit Registered Research Agency

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