Jeff Squyres wrote:
On Jan 18, 2006, at 9:02 PM, Paul Greidanus wrote:
I've got a new cluster I'm deploying (with trunk ~4105), and I had a
question that came up:
My nodes are 4 and 8 core (8 and 32Gb RAM), and we were wondering if
LAM was compiled to take advantage of the interconnect
(hypertransport) between CPUs, or does it use the IP stack/network to
connect for cpus on the same machine?
LAM has less-than-optimal IB support, but it is functional. We have not
expressly tested on machines with hypertransport -- I actually don't
know if they export normal HCA interfaces (which LAM can support) or
whether a hypertransport-enabled MPI is required.
Ok, can I s/hypertransport/SMP/g on the message, which is more what I'm
thinking of.. the details of the memory subsys inside of a machine
aren't really all that important to this question.. but, will the LAM
that comes with Oscar use mem->mem copies, rather then using the IP
stack, or even worse, send it out to the network device itself?
Also, is it usually preferable to fill up a node, rather then spread
it out across the nodes? i.e. 16 cpu job over 16 nodes, or 2 8 cpu
nodes?
It is usually preferable to fill up a node before spreading to a second
node because latencies between processors can be smaller (e.g., via
using shared memory, or even using the HCA's DMA engine).
Cool, that's what I was thinking too.
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