HI Gary, The decision occurs within the MPI processes themselves (during the call to MPI_Init) - so after the orte daemons have started on the nodes.
The BTL's report their "latency" and "bandwidth" - up the stack to the PML/BML layer which then decides based on these metrics which BTL to use to send/recv messages between any given pair of MPI ranks. Hope this helps, Howard 2014-12-23 13:29 GMT-07:00 Gary Jackson <ga...@cs.umd.edu>: > > I'm not having any trouble getting it to start, and it's definitely using > the openib btl. I was just wondering how it decided whether the openib btl > was appropriate before going down the btl list to tcp when all mpirun gets > is a hostname and no other information about connectivity on the remote > end. For instance, is this determined before or after orted runs on the > remote end? > > On 12/23/14, 2:18 PM, Howard Pritchard wrote: > >> Hello Gary, >> >> It depends on how the Open MPI was built, and on mca parameters passed >> to the job either via settings in an mca params conf >> file or the mpirun command line or env. variables. If you have mxm >> (MLNX) or psm (qlogic/intel) installed on the system >> where your open mpi was built, you may actually be using one of those >> via the MTL path. >> >> Try >> >> mpirun -np 2 -H hosta,hostb -mca btl self,vader,openib >> ./your_favorite_test >> >> That should force open mpi to try using openib between the pair of >> hosts. Note you don't need "vader" on the command line >> if you are running only one mpi rank/node. >> >> Howard >> >> >> >> >> 2014-12-23 11:48 GMT-07:00 Gary Jackson <ga...@cs.umd.edu >> <mailto:ga...@cs.umd.edu>>: >> >> >> How does OpenMPI decide whether to use the IB BTL between a given >> pair of hosts, assuming there is an IB interface available? >> >> -- >> Gary >> _________________________________________________ >> users mailing list >> us...@open-mpi.org <mailto:us...@open-mpi.org> >> Subscription: http://www.open-mpi.org/__mailman/listinfo.cgi/users >> <http://www.open-mpi.org/mailman/listinfo.cgi/users> >> Link to this post: >> http://www.open-mpi.org/__community/lists/users/2014/12/__26063.php >> <http://www.open-mpi.org/community/lists/users/2014/12/26063.php> >> >> >> >> >> _______________________________________________ >> users mailing list >> us...@open-mpi.org >> Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users >> Link to this post: http://www.open-mpi.org/community/lists/users/2014/12/ >> 26064.php >> >> > > -- > Gary > _______________________________________________ > users mailing list > us...@open-mpi.org > Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users > Link to this post: http://www.open-mpi.org/community/lists/users/2014/12/ > 26065.php >
