I have implemented some algorithms in C++ which are greatly affected by
shuffling time among nodes which is done by some broadcast calls. Up to
now, I have been testing them by running something like
mpirun -mca btl ^openib -mca plm_rsh_no_tree_spawn 1 ./my_test
which I think make MPI_Bcast to
Konstantinos,
I am afraid there is some confusion here.
the plm_rsh_no_tree_spawn is only used at startup time (e.g. when remote
launching one orted daemon per node but the one running mpirun).
there is zero impact on the performances of MPI communications such as
MPI_Bcast()
the
Thanks for clarifying that Gilles.
Now I have seen that omitting "-mca plm_rsh_no_tree_spawn 1" requires
establishing passwordless SSH among the machines but this is not required
for setting "--mca coll_tuned_bcast_algo". Is this correct or am I missing
something?
Also, among all possible
If you use the rsh tree spawn mechanism, then yes, any node must be able
to SSH passwordless to any node.
This is only used to spawn one orted per node.
when the number of nodes is important, a tree spawn is faster and avoids
having all the SSH connections issued and maintained from the
node
