MKL threading

[kkm000]

MKL threading

[eddelbuettel]

The details now escape me :-/ but IIRC this goes back to a tip I got from an Intel engineer from one of their labs -- it may have been in the context of RcppParallel (which uses TBB). I don't recall now - I seem to remember that it was related to using the GNU toolchain (as common in Linux) along with the MKL (rather than Intel's compiler, IIRC).

Edit: Maybe it was this thread: #2. And more here: c6d8d84. I suggest you talk more to Intel.

[kkm000]

I think what the script is doing is exactly right, provided that the users are familiar with the peculiarities of MKL threading: changing the default from the multithreaded iomp5 to, multithreaded again, GOMP-based implementation. On the other hand, it may have a surprising effect on performance if someone is using it simply as an alternative to generic single-threaded BLAS libraries. MKL_THREADING_LAYER=sequential (no automatic multithreading) may potentially be a safer default for the general user for two reasons: (1) it does not load any OMP libraries into the process, so no possible conflicts like in #2 with GCC -fopenmp, and (2) automatic multithreading with MKL is not necessarily always the best choice.

It's possible that I'm confused, not understanding the intended audience for this script. I was just too impressed with your update-alternatives idea not to read the whole script, and thought maybe sharing this tidbit would be helpful. Again, sorry if you feel I'm just wasting your time.

[andrewjholbrook]

@kkm000 Thanks for the information, MKL_THREADING_LAYER=sequential is faster than default is faster than MKL_THREADING_LAYER=GNU on my machine.