[Beowulf] Better C2D or Quadcore

[Chris Samuel]

On Wed, 28 Nov 2007, amjad ali wrote:

> high per-CPU memory performance. Each CPU (core in dual core
> systems) needs to have its own memory bandwith of roughly 2 or more
> gigabytes.

If this is indeed the case for your problems then you might find that 
quad core systems don't cut it - a contact of mine at another 
institution asked me to do some Ramspeed benchmarks to compare our 
1.9GHz Barcelona test system to their Clovertown cluster nodes.

They were measuring about 5GB/s aggregate RAM bandwidth when running 
the same test on all 8 cores (around 650MB/s per core) whereas we 
were seeing over 12MB/s aggregate.

Yesterday we upgraded that to a 2.1GHz test system and the measured 
bandwidth increased to just over 13GB/s.

The nice thing about this test is that the benchmark code is written 
in assembler so the compiler doesn't matter.

Running the streams benchmark in OpenMP mode with 8 threads agrees 
with those numbers on the 1.9GHz Barcelona (when compiled with Intel 
or PGI, much lower speeds with GCC).  I don't have a note of the 
numbers for the 2.1GHz chips with me on the train.

PGI 7.1-1 : pgcc -mp -fastsse -tp barcelona-64,k8-64 -Mipa=fast -o 
stream ./stream.c

Function      Rate (MB/s)   Avg time     Min time     Max time
Copy:       12261.7219       0.1044       0.1044       0.1045
Scale:      12284.4198       0.1042       0.1042       0.1043
Add:        12213.4179       0.1574       0.1572       0.1581
Triad:      11875.6082       0.1619       0.1617       0.1621

Intel v10 : icc -static-intel -openmp -O5 -o stream-icc stream.c

Function      Rate (MB/s)   Avg time     Min time     Max time
Copy:       12214.5757       0.1048       0.1048       0.1050
Scale:      12155.7238       0.1054       0.1053       0.1055
Add:        12243.4062       0.1569       0.1568       0.1570
Triad:      12240.2984       0.1569       0.1569       0.1570

cheers,
Chris
-- 
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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