Re: [OMPI users] question about "--rank-by slot" behavior

2016-11-30 Thread David Shrader
Thank you for the explanation! I understand what is going on now: there is a process list for each node whose order is dependent on the mapping policy, and the ranker, when using "slot," walks through that list. Makes sense. Thank you again! David On 11/30/2016 04:46 PM, r...@open-mpi.org wro

Re: [OMPI users] question about "--rank-by slot" behavior

2016-11-30 Thread r...@open-mpi.org
“slot’ never became equivalent to “socket”, or to “core”. Here is what happened: *for your first example: the mapper assigns the first process to the first node because there is a free core there, and you said to map-by core. It goes on to assign the second process to the second core, and the th

Re: [OMPI users] question about "--rank-by slot" behavior

2016-11-30 Thread David Shrader
Hello Ralph, I do understand that "slot" is an abstract term and isn't tied down to any particular piece of hardware. What I am trying to understand is how "slot" came to be equivalent to "socket" in my second and third example, but "core" in my first example. As far as I can tell, MPI ranks s

Re: [OMPI users] question about "--rank-by slot" behavior

2016-11-30 Thread r...@open-mpi.org
I think you have confused “slot” with a physical “core”. The two have absolutely nothing to do with each other. A “slot” is nothing more than a scheduling entry in which a process can be placed. So when you --rank-by slot, the ranks are assigned round-robin by scheduler entry - i.e., you assign

[OMPI users] question about "--rank-by slot" behavior

2016-11-30 Thread David Shrader
Hello All, The man page for mpirun says that the default ranking procedure is round-robin by slot. It doesn't seem to be that straight-forward to me, though, and I wanted to ask about the behavior. To help illustrate my confusion, here are a few examples where the ranking behavior changed ba