On Wed, 1 Jul 2020 at 20:13, Susi Lehtola <jussileht...@fedoraproject.org> wrote: > > On Wed, 1 Jul 2020 10:54:16 -0600 > Jerry James <loganje...@gmail.com> wrote: > > > On Wed, Jul 1, 2020 at 10:26 AM Iñaki Ucar <iu...@fedoraproject.org> > > wrote: > > > BTW, I would also like to discuss here, as part of this proposal, > > > which backend should be the system-wide default. I believe we all > > > would agree that OpenBLAS nowadays is the best choice. But then, the > > > serial or the openmp version? > > > > First, I want to make sure I understand the current openblas > > packaging. Is this correct? > > > > openblas-openmp: use if the application uses OpenMP > > Yes; then OpenBLAS calls get run in parallel in single-threaded regions > of the code, and if sequential mode in regions that are already > running parallel. > > > openblas-serial: use if the application is multithreaded > > openblas-threads: use if the application is single-threaded > > No, this is exactly the wrong way around. You should use the serial > library for code that you want to be running in serial (this way you > can get several instances of the program running efficiently), and the > pthreads version if you want to run the BLAS/LAPACK regions in parallel > (but are somehow opposed to OpenMP!)..
I think I'm more confused than before. :D > > The question of the default is a hard one. What happens if a > > multithreaded application that does not use OpenMP is linked with the > > OpenMP build of OpenBLAS? > > Then you get too much parallellism, i.e. every call to OpenBLAS will > launch several threads, and this will naturally ruin your scaling. So would you say that openblas-serial is the most sensible system-wide default? -- Iñaki Úcar _______________________________________________ devel mailing list -- devel@lists.fedoraproject.org To unsubscribe send an email to devel-le...@lists.fedoraproject.org Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org
