Prior to this commit we matched local interfaces to remote interfaces in
order to create endpoints in a simplistic way. If any remote interfaces
were on the same subnet as any of our local interfaces then only local
interfaces would be paired (IP-routed remote interfaces would be
ignored).
This commit introduces a more general scheme which attempts to make the
"best" pairing of local interfaces to remote interfaces. We now cast
the problem as a graph theory problem known as the "Assignment Problem",
or finding a maximum-cardinality, minimum-weight bipartite matching. We
solve this problem by reducing the bipartite graph of interface
connectivity to a flow network and then solving for a minimum cost flow.
This is then easily converted into back into a matching on the original
bipartite graph.
In the new scheme, interfaces on the same subnet are preferred over
interfaces requiring intermediate routing hops and higher bandwidth
links are preferred over lower bandwidth links.
Reviewed-by: Jeff Squyres <jsquyres@cisco.com>
cmr=v1.7.5:ticket=trac:4253
This commit was SVN r30849.
The following Trac tickets were found above:
Ticket 4253 --> https://svn.open-mpi.org/trac/ompi/ticket/4253
This functionality is required for routable UDP/IP usnic traffic.
Previously we would only setup endpoints for remote interfaces on the
same subnet as the current module's local interface. This behavior
still holds if two processes share any common subnets. However, if the
two processes only have no subnets in common then we assume that all
interfaces are reachable from all other interfaces and wire them up in a
1-1, randomly-matched order somewhat similarly to the "tcp" BTL's
behavior.
Only match in different subnets if we detect UDP support in the lower
layer.
Reviewed-by: Jeff Squyres <jsquyres@cisco.com>
cmr=v1.7.5:ticket=trac:4253
This commit was SVN r30839.
The following Trac tickets were found above:
Ticket 4253 --> https://svn.open-mpi.org/trac/ompi/ticket/4253
Brian (rightfully) hit me on the head with the
don't-use-ORTE-use-the-rte-framework clue bat; the usnic BTL now
nicely plays with the RTE framework.
This commit was SVN r28907.
This BTL accesses the Cisco usNIC Linux device via the Linux verbs
API via Unreliable Datagram queue pairs. A few noteworthy points:
* This BTL does most of its own fragmentation; it tells the PML that
it has a very high max_send_size (much higher than the network
MTU).
* Since UD fragments are, by definition, unreliable, the usnic BTL
handles all of its own reliability via a sliding window approach
using the opal_hotel construct and many tricks stolen from the
corpus of knowledge surrounding efficient TCP.
* There is a fun PML latency-metric based optimization for NUMA
awareness of short messages.
* Note that this is ''not'' a generic UD verbs BTL; it is specific to
the Cisco usNIC device.
This commit was SVN r28879.
