On 07/10/2012 05:31 PM, Jeff Squyres wrote:
+1. Also, not all Ethernet switches are created equal --
particularly commodity 1GB Ethernet switches.
I've seen plenty of crappy Ethernet switches rated for 1GB
that could not reach that speed when under load.
Are you perhaps belittling my dear $43 [brand undisclosed]
5-port GigE SoHo switch, that connects my Pentium-III
toy cluster, just because it drops a few packages [per microsec]?
It looks so good, with all those fiercely blinking green LEDs.
Where else could I fool around with cluster setup and test
the OpenMPI new releases? :)
The production cluster is just too crowded for this,
maybe because it has a decent
HP GigE switch [IO] and Infiniband [MPI] ...
Gus
On Jul 10, 2012, at 10:47 AM, Ralph Castain wrote:
I suspect it mostly reflects communication patterns. I don't know anything
about Saturne, but shared memory is a great deal faster than TCP, so the more
processes sharing a node the better. You may also be hitting some natural
boundary in your model - perhaps with 8 processes/node you wind up with more
processes that cross the node boundary, further increasing the communication
requirement.
Do things continue to get worse if you use all 4 nodes with 6 processes/node?
On Jul 10, 2012, at 7:31 AM, Dugenoux Albert wrote:
Hi.
I have recently built a cluster upon a Dell PowerEdge Server with a Debian 6.0
OS. This server is composed of
4 system board of 2 processors of hexacores. So it gives 12 cores per system
board.
The boards are linked with a local Gbits switch.
In order to parallelize the software Code Saturne, which is a CFD solver, I
have configured the cluster
such that there are a pbs server/mom on 1 system board and 3 mom and the 3
others cards. So this leads to
48 cores dispatched on 4 nodes of 12 CPU. Code saturne is compiled with the
openmpi 1.6 version.
When I launch a simulation using 2 nodes with 12 cores, elapse time is good and
network traffic is not full.
But when I launch the same simulation using 3 nodes with 8 cores, elapse time
is 5 times the previous one.
I both cases, I use 24 cores and network seems not to be satured.
I have tested several configurations : binaries in local file system or on a
NFS. But results are the same.
I have visited severals forums (in particular
http://www.open-mpi.org/community/lists/users/2009/08/10394.php)
and read lots of threads, but as I am not an expert at clusters, I presently do
not see where it is wrong !
Is it a problem in the configuration of PBS (I have installed it from the deb
packages), a subtile compilation options
of openMPI, or a bad network configuration ?
Regards.
B. S.
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