[petsc-dev] GAMG error with MKL

[Smith, Barry F.]

> On Jul 5, 2018, at 8:28 AM, Mark Adams <mfadams at lbl.gov> wrote:
> 
> 
> Please share the results of your experiments that prove OpenMP does not improve performance for Mark’s users. 
> 
> This obviously does not "prove" anything but my users use OpenMP primarily because they do not distribute their mesh metadata.

   I.e. my users have decided not to write scalable code. 

> They can not replicated the mesh on every core,
> on large scale problems and shared memory allows them to survive. They have decided to use threads as opposed to MPI shared memory. (Not a big deal, once you decide not to use distributed memory the damage is done and NERSC seems to be OMP centric so they can probably get better support for OMP than MPI shared memory.)
> 
> BTW, PETSc does support OMP, that is what I have been working on testing for the last few weeks. First with Hypre (numerics are screwed up from an apparent compiler bug or a race condition of some sort; it fails at higher levels of optimization), and second with MKL kernels. The numerics are working with MKL and we are working on packaging this up to deliver to a user (they will test performance).
>