I stumbled upon something while using 'ps -eFL' to view threads of processes, and Google searches have failed to answer my question. This question holds for OpenMPI 1.6.x and even OpenMPI 1.4.x.
For a program which is pure MPI (built and run using OpenMPI) and does not implement Pthreads or OpenMP, why is it that each MPI task appears as having 3 threads: UID PID PPID LWP C NLWP SZ RSS PSR STIME TTY TIME CMD sasso 20512 20493 20512 99 3 187849 582420 14 11:01 ? 00:26:37 /home/sasso/mpi_example.exe sasso 20512 20493 20588 0 3 187849 582420 11 11:01 ? 00:00:00 /home/sasso/mpi_example.exe sasso 20512 20493 20599 0 3 187849 582420 12 11:01 ? 00:00:00 /home/sasso/mpi_example.exe whereas if I compile and run a non-MPI program, 'ps -eFL' shows it running as a single thread? Granted the CPU utilization (C) for 2 of the 3 threads is zero, but the threads are bound to different processors (11,12,14). I am curious as to why this is, and no complaining that there is a problem. Thanks! --john
