Specify the Number of Processes

Use the -n argument to specify the number of processes to run. This argument can be used in concert with the bsub -n argument to cause process wrapping to occur. Process wrapping is the term used to describe a technique for distributing multiple processes to fewer processors than there are processes. As a result, each processor has multiple processes, which are spawned in a cyclical, wrap-around, fashion.

For example, the following will distribute 48 processes across 16 processors, resulting in a 3-process wrap per processor.

hpc-demo% bsub -I -n 16 -q hpc -sunhpc -n 48 hpc-job

If you specify a range of processors rather than a single quantity and a larger number of processes, the process wrapping ratio (number of processes per to processor) will depend on the number of processors that are actually allocated.

For example, the following will distribute 48 processes across at least 8 processors and possibly as many as 16.

hpc-demo% bsub -I -n 8,16 -q hpc -sunhpc -n 48 hpc-job

Consequently, the process-to-processor wrapping ratio may be as high as 6:1 (48 processes across 8 processors) or as low as 3:1 (48 processes across 16 processors).