Scaling issue run openmp on a cluster

[AIBSCT80]

Scaling issue run openmp on a cluster

[jsquyres]

I'm afraid that there isn't enough information here to definitively say what is going on.

• Your application might well be bound to a single core; running multiple threads bound to that one core may cause contention.
• Your application may simply not be scalable -- i.e., the overhead of splitting the work up into multiple threads and then gathering all the results may overwhelm the benefit of having multiple workers
• You are testing over an incredibly small amount of work. Increase your workload to get more realistic results (e.g., if the overheads of splitting / gathering are [more or less] fixed, increasing the amount of work for each thread can dramatically improve the efficiency).

[AIBSCT80]

@jsquyres thanks. it seems to me the threads are binded to one core. There is no scalability.

[jsquyres]

I'm not quite sure how to parse your reply.

You didn't provide answers to the templated questions in the github issue, so I don't know what version you're running. If it's Open MPI v5, you can see https://docs.open-mpi.org to see how to set process binding.

Does that resolve your question?

[rhc54]

The problem lies in the salloc cmd line - you asked for 1 cpu, and that's what you were given.