[Beowulf] Re: More cores/More processors/More nodes?

[Håkon Bugge]

At 04:47 03.10.2006, beowulf-request at beowulf.org wrote:
Greg Lindahl wrote:
 > On Thu, Sep 28, 2006 at 07:06:14PM +0100, Peter Wainwright wrote:
 >
 >
 >> What (in your opinion) is the right tradeoff between more cores,
 >> more processors and more individual compute nodes?
 >
 > $/performance.
 >
 > Once you have your code written into pure MPI form, then you can run
 > on any of the above alternatives. Then you can simply work out
 > the price for various things, and make a guess at the performance.
 > Run a few benchmarks to check your guesses.

On two-socket, dual core Opteron systems, we 
often see that throughput is enhanced by using 
two times two processes per node. For example, if 
you're running jobs with 16 processes on an 
eight-node cluster, 8x2 plus 8x2 is faster than 
4x4 and 4x4 (nnodesxppn). But gain depends on 
flexibility of process-to-processor mapping of 
the MPI used. Some apps like to use as few 
sockets as possible, whereas others like the opposite ;-)


Håkon