On Wed, 1 Jul 2020 21:03:09 -0600 Jerry James <loganjerry@xxxxxxxxx> wrote: > On Wed, Jul 1, 2020 at 12:06 PM Susi Lehtola > <jussilehtola@xxxxxxxxxxxxxxxxx> wrote: > > On Wed, 1 Jul 2020 10:54:16 -0600 > > Jerry James <loganjerry@xxxxxxxxx> wrote: > > > 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!).. > > Okay, I think the wiki's wording is hard to understand > (https://github.com/xianyi/OpenBLAS/wiki/faq#multi-threaded), at least > for me. Let me see if I've got this straight. > > 1. openblas-opemp computes on subranges in parallel using OpenMP > 2. openblas-threads computes on subranges in parallel using pthreads > 3. openblas-serial uses a single thread for the entire computation > > Right? Exactly. But the key bit here is that if openblas-openmp is called within a code segment that is already OpenMP parallel, then OpenBLAS does not parallellize further: if you have 8 cores, and the program is running on 8 threads, further parallellism (going to 8*8=64 threads) would just ruin the performance. > What I'm looking for is a set of rules I can apply when I've got a > package that uses BLAS, but upstream has given no guidance on what > kind of BLAS library is suitable. I've got several of those, so I > want to check that they're linking with the best version of the > library. How should I make that determination? Also, how do I know > whether to use, say, openblas-openmp vs. openblas-openmp64 vs. > openblas-openmp64_? openblas-openmp is generally the safe choice. As for the latter question, it depends on whether you compile your code with 4-bit or 8-bit integers. -- Susi Lehtola Fedora Project Contributor jussilehtola@xxxxxxxxxxxxxxxxx _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx 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@xxxxxxxxxxxxxxxxxxxxxxx
