Re: [Gretl-users] Issue with openBLAS, openMPI and pthreads

Am 05.06.2017 um 14:55 schrieb Allin Cottrell: > On Sat, 3 Jun 2017, Artur Tarassow wrote: > >> Damn, I thought it's solved. Even though MPI is now correctly >> configured, I still obtain the following message: >> >> <gretlcli> >> *** Warning *** >> * >> * gretl is built using OpenMP, but is linked against >> * OpenBLAS parallelized via pthreads. This combination >> * of threading mechanisms is not recommended. Ideally, >> * OpenBLAS should also use OpenMP. >> >> </gretlcli> > > This is basically nothing to do with MPI. It's to do with the > possibility that "raw" pthreads and OpenMP end up being invoked > concurrently, in which case the result is unpredictable but probably bad! > > Various functions in gretl are parallelized via OpenMP (which is much > easier to program than low-level pthreads). If such a function happened > to call a BLAS routine, and that routine was parallelized in OpenBLAS > using pthreads rather than OpenMP, nasty things could happen (two > thread-management mechanisms in competition). And one way of ensuring > that can never happen is to ensure that OpenBLAS is itself parallelized > using OpenMP (which is a build-time option). That's why we say, "Ideally > OpenBLAS should also use OpenMP". > > However... in fact we can probably get rid of the warning above, since > we've been over the libgretl functions which invoke OpenMP, and I think > we ensured that OpenBLAS-pthreads will not get called either directly or > indirectly by those functions. Nonetheless, I think it's good practice > to set things up so that any given program is never going to invoke > pthreads and OpenMP simultaneously. > > Allin Cottrell Thanks for this clarification, Allin. So in case I want to get 100% sure that I use OpenMP rather than pthreads, I should re-compile OpenBLAS myself with the correct build-time option [...]

as it remains unclear which one the Ubuntu-maintainer used, right?