#530: Change default for --num-threads --------------------------+------------------------------------------------- Reporter: eschnett | Owner: hinder Type: enhancement | Status: assigned Priority: major | Milestone: Component: SimFactory | Version: Resolution: | Keywords: --------------------------+-------------------------------------------------
Comment (by eschnett):
I am afraid that we are here over-designing something that is not really a problem at all. Do we know even of a single case where someone would be severely affected by changing the default?
We don't go through these hoops when it comes to MPI processes. There is no "this thorn doesn't do MPI" flag. If a thorn can't handle MPI, it would check this at startup, and abort with an error. We could do the same with OpenMP, except that OpenMP is "backward compatible" in the sense that it doesn't break anything, it would just run a bit slower than naively expected.
Having a single thorn disable OpenMP for a whole simulation is overkill. The thorn will still work fine with OpenMP. Whether this is acceptable or not depends on the user's settings and the user's expectations. Is there a thorn which should disable OpenMP today? Which would it be? AHFinderDirect comes to my mind... When it comes to performance problems, then e.g. CarpetIOASCII is a much bigger sinner with it's missing MPI parallelisation (it serialises output).
I think we are just being afraid of taking this step. We are imagining problems, trying to design a perfect solution, and in the process complicate things for everybody and avoid progress for everybody. Let's just do it, and if it doesn't work out, let's listen to the complaints and address them. This is the development version, after all.