[Gretl-devel] Re: MPI and OpenMP (and openblas?)
Am 16.01.2020 um 16:13 schrieb Marcin Błażejowski:
On 16.01.2020 12:46, Sven Schreiber wrote:
>> But the fact is that in many cases some routines runs in parallel via
>> OpenMP no matter what is the value of "omp_num_threads". I remember
that
>> 2-3 years ago Jack explained me that some algebra stuff lauch OpenMP
>> automagically.
> Aha, that would explain it. But the question is, is it a bug? I mean if
> we want to suppress multithreading, we want to do that also in the
> openblas context, no?
I believe, yes.
BTW, this here might also be relevant:
https://github.com/xianyi/OpenBLAS/issues/1653
Using the settings:
OMP_NUM_THREADS 4
OMP_PLACES "{0,1,2,3}"
OMP_PROC_BIND spread
If I understand correctly, just limiting OMP_NUM_THREADS alone is in
general no guarantee that hyperthreading is prevented.
Whether that makes a practical difference, I don't know (yet).
cheers
sven