Kewl!
I added ticket 1277 so that we are sure to document this for v1.3.
On Apr 23, 2008, at 11:09 AM, Ralph H Castain wrote:
I added a new "loadbalance" feature to OMPI today in r18252.
Brief summary: adding --loadbalance to the mpirun cmd line will
cause the
round-robin mapper to balance your specified #procs across the
available
nodes.
More detail:
Several users had noted that mapping byslot always caused us to
preferentially load the first nodes in an allocation, potentially
leaving
other nodes unused. If they mapped bynode, of course, this wouldn't
happen -
but then they were forced to a specific rank-to-node relationship.
What they wanted was to have the ranks numbered byslot, but to have
the ppn
balanced across the entire allocation.
This is now supported via the --loadbalance cmd line option. Here is
an
example of its affect (again, remember that loadbalance only impacts
mapping
byslot):
no-lb lb bynode
node0: 0,1,2,3 0,1,2 0,3,6
node1: 4,5,6 3,4 1,4
node2: 5,6 2,5
As you can see, the affect of --loadbalance is to balance the ppn
across all
the available nodes while retaining byslot rank associations. In
this case,
instead of leaving one node unused, we take advantage of all available
resources.
Hope this proves helpful
Ralph
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Jeff Squyres
Cisco Systems
