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Will submit an OpenMPI job (-a mympi) requesting 12 processors (-n 12) spanned all on one host (-R "span[hosts=1]") to the psanaq batch queue (-q psanaq).

bsub "psana1503 psana1509" -q psnehq -a mympi -n 12 -o ~/output/%J.out ~/bin/hello

Will submit an OpenMPI job (-a mympi) requesting 12 processors (-n 12) on two nodes (psana1503 and psana1509) to the psnehq batch queue (-q psnehq).

When no ptile is specified in the resource string, the batch system will add "span[ptile=12]". Running MPI jobs on as few hosts as possible helps optimize MPI communication between ranks, and minimize job failure due to an error with a host. However it does mean more ranks sharing per host resources, such as memory and I/O. Care is required when managing host resources for your job by specifying your own ptile. If jobs from different users (or the same user) have different ptile settings, the batch system will not run these jobs on the same host, which may lead to under-utilization of the batch queue. For instance, if one user specifies -R "span[ptile=4]" -n 2, taking two ranks on hostA, the system will not put ranks from other user jobs on hostA, unless they also specify span[ptile=4] (in particular the default resource string of [ptile=12]  excludes other jobs from hostA.

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