Ralph,
I am not using the TCP BTL, only OPENIB one. Does this change the
number of sockets in use per node, please ?
But I suspect the ORTE daemons are communicating only through TCP
anyway, right ?
Also, is there anybody in the OpenMPI team using an SGI Altix cluster
with a high number of nodes
(1k nodes, ie 8k cores) that I could ask him (her) about the right setup ?
Thanks, Best, G.
Le 15/12/2010 21:03, Ralph Castain a écrit :
On Dec 15, 2010, at 12:30 PM, Gilbert Grosdidier wrote:
Bonsoir Ralph,
Le 15/12/2010 18:45, Ralph Castain a écrit :
It looks like all the messages are flowing within a single job (all three
processes mentioned in the error have the same identifier). Only possibility I
can think of is that somehow you are reusing ports - is it possible your system
doesn't have enough ports to support all the procs?
Seems there is on every worker node a range of almost 30k ports available:
ssh r33i0n0 cat /proc/sys/net/ipv4/ip_local_port_range
32768 61000
This is AFAIK the only way I can get info about this.
Are these 30k ports this enough ?
Depends on how many nodes there are in your system.
Question is : is OpenMPI opening ports from every node towards every other node
?
In such a case I could figure out why it is going to to lacking ports when
I increase the number of nodes.
Yes - in two ways:
1. each ORTE daemon opens a port to every other daemon in the system. Thus, you
need at least M ports if your job is running across M nodes
2. each MPI process will open a direct port to any other MPI process that it
communicates with. So if you have N processes on a node, and they only
communicate to the 8 nearest neighbor nodes (each of which have N processes),
and you are using the TCP btl, then you will consume an additional 8*N*N
sockets on each node.
But: is there a possibility (mca param ?) to prevent OpenMPI to open so many
ports ?
Indeed, apart from rank 0 node, every MPI process will need to communicate with
ONLY
the 8 (nearest) neighbour nodes. So, there should be a switch somewhere telling
OpenMPI
to open a port ONLY when needed, but I did not find it among ompi_info stuff ;-)
It always only opens a port when something tries to communicate - we never open
ports in advance.
Which one is it ?
Thanks, Best, G.
