[Beowulf] thermal/power limits

Douglas Eadline deadline at eadline.org
Mon Aug 12 09:34:54 PDT 2013


> Potentially, of course, once you bite the bullet to parallelize, and you
> do it in a scalable manner, then, you can presumably scale to
> architectures where you have N cores running at full speed (e.g. A classic
> cluster).  I wonder, though, whether the end-user applications codes
> actually do that, or whether they design for the "single user on a single
> box" model.  That is, they design to use multiple cores in the same
> box,but don't really design for multiple boxes, in terms of concurrency,
> latency between nodes, etc.

This in my mind is not an easy question to answer. Assuming
an application can use more cores in a scalable fashion,
the issue with SMP multi-core is how many effective cores
you get vs actual -- due to memory contention.
In my tests "it all depends on the application"
One of the nice things about MPI codes is the ability to run
on 16 separate nodes, one 16-way node, or anything in between.
OpenMP has no way to get off the motherboard, but soon will open
the door the onboard SIMD units. OpenMP does not guarantee
an automatic win over MPI on multi-core either.


> James Lux, P.E.
> Task Manager, FINDER – Finding Individuals for Disaster and Emergency
> Response
> Co-Principal Investigator, SCaN Testbed (née CoNNeCT) Project
> Jet Propulsion Laboratory
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