Hi,
the hostnames (or their IPs) are only used to ssh orted.
if you use only the tcp btl :
TCP *MPI* communications (vs OOB management communications) are handled
by btl/tcp
by default, all usable interfaces are used, then messages are split
(iirc, by ob1 pml) and then "fragments"
are sent using all interfaces.
each interface has a latency and bandwidth that is used to split message
into fragments.
(assuming it is correctly configured, 90% of a large message is sent
over the 10GbE interface, and 10% is sent over the GbE interface)
if you can explicitly list/blacklist interface
mpirun --mca btl_tcp_if_include ...
or
mpirun --mca btl_tcp_if_exclude ...
(see ompi_info --all for the syntax)
but if you use several btls (for example tcp and openib), the btl(s)
with the lower exclusivity are not used.
(for example, a large message is *not* split and send using native ib,
IPoIB and GbE because the openib btl
has a higher exclusivity than the tcp btl)
did this answer your question ?
Cheers,
Gilles
On 4/8/2016 12:24 PM, dpchoudh . wrote:
Hello all
(Newbie warning! Sorry :-( )
Let's say my cluster has 7 nodes, connected via IP-over-Ethernet for
control traffic and some kind of raw verbs (or anything else such as
SRIO) interface for data transfer. Let's say my host file chooses 4
out of the 7 nodes for an MPI job, based on the IP address, which are
assigned to the Ethernet interfaces.
My question is: where in the code does this mapping between
IP-to-whatever_interface_is_used_for_MPI_Send/Recv is determined, such
as only those chosen nodes receive traffic over the verbs interface?
Thanks in advance
Durga
We learn from history that we never learn from history.
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