On 10/01/2015 09:27 AM, Orion Poplawski wrote:
We may be looking a getting a couple new compute nodes. I'm leery
though of
going too high in processor core counts. Does anyone have any general
experiences with performance scaling up to 12 cores per processor with
general
models like CM1/WRF/RAMS on the current crop of Xeon processors?
Lately I have been working on a system with >512Gb of RAM and a lot of
processors.
This wouldn't be at all a cost effective beowulf node, but it is a
godsend when the problems being addressed require huge amounts of memory
and do not partition easily to run on multiple nodes. The one I'm using
is NUMA rather than SMP, and careful placement of the data with respect
to the nodes is sometimes required for optimal performance. That is
likely to be the case on some of the machines you may be looking at.
One must also be careful using multiple processors on this machine
because some of them share cache, and others don't, so that adding too
many processes in the wrong place can reduce throughput because these
start having to go to slower main memory inside tight loops. Some of
this is discussed in this longish thread:
http://www.beowulf.org/pipermail/beowulf/2015-July/033263.html
This machine is also prone to locking up (to the point it doesn't answer
terminal keystrokes from a remote X11 terminal) when writing huge files
back to disk. I have not tracked this one down yet, it seems to be
related to unmapping a memory mapped 10.5 Gb file. A bit difficult to
debug because when it is happening it isn't possible to look at what the
machine is doing.
Regards,
David Mathog
[email protected]
Manager, Sequence Analysis Facility, Biology Division, Caltech
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