#1850: Severe performance problem on Stampede -------------------------+-------------------------------------------------- Reporter: hinder | Owner: Type: defect | Status: confirmed Priority: major | Milestone: Component: SimFactory | Version: development version Resolution: | Keywords: -------------------------+--------------------------------------------------
Comment (by eschnett):
The description of KMP_AFFINITY was clearly written by a professional documentation writer who knows how to write a lot of text while introducing sufficient ambiguity to not even be wrong.
As I mentioned above, setting this variable (when not using SystemTopology) is probably wrong unless there is only one MPI process per node. Please read my description above, and say what it is unclear if you don't understand it; I won't repeat it here.
Yes, we all agree that the default options should be better. There are two options:
(1) Examine all possible "reasonable" configurations (MPI processes per node, OpenMP threads per process), and ensure that the new setting work fine in all cases (2) Examine only a subset of configurations, and ensure that things don't change except for these configurations, using appropriate if-statements in the submit script.
I mentioned earlier that I am regularly running benchmarks on a variety of systems. Of course I am using SystemTopology, so I didn't notice this problem. I usually run multiple benchmarks for multiple configurations (MPI processes / OpenMP threads) to find the optimum configuration.