[mvapich-discuss] MPI_Comm_spawn always uses just 1 host

[Rutger Hofman]

Good afternoon list,

I want to control the hosts on which processes are spawned by 
MPI_Comm_spawn.

But in our cluster (DAS4 http://www.das4.cs.vu.nl RHEL6 w/ QDR Mellanox 
Infiniband), a call to MPI_Comm_spawn() does spawn processes, but they 
always all run on one single host (something like rank (n+1)%size when I 
do -np n).

Behaviour is the same whatever MPI_Info properties I specify to the 
MPI_Comm_spawn() call:
   "host" "node048"
   "hostfile" "hostfile"
   "hosts" "node048 node049 node050"
etc etc. None of them generates an error; does that mean they are 
actually valid?

My mpirun_rsh incantation is something like
$ mpirun_rsh -ssh -np 3 -hostfile hostfile \
       MV2_SUPPORT_DPM=1 ./spawn ./slave
and, as stated, slave instances do run, only I have no control where.

I tried the mvapich2-1.6 packaged with our cluster, and a freshly 
downloaded mvapich2-1.8a2. The behaviour is the same.

In the source code I see mention of -spawnfile. This option is rejected 
by mpirun_rsh.

So, my question: how can I specify the set of hosts that processes 
should be spawned on?

Thanks,

Rutger Hofman
VU Amsterdam