Quick method for estimating walltime

For Torque / OpenPBS or any other scheduler, walltime is a important parameter to allow the scheduler to determine how long the jobs will take. You can do a quick rough estimate by using the command time

# time -p mpirun -np 16 --host node1,node2 hello_world_mpi

real 4.31
user 0.04
sys 0.01

Use the value of 4:31 as the estimate walltime. Since this is an estimate, you may want to place a higher value in the walltime

$ qsub -l walltime=5:00 -l nodes=1:ppn=8 openmpi.sh -v file=hello_world