[petsc-dev] GAMG error with MKL

[Matthew Knepley]

On Thu, Jul 5, 2018 at 2:04 PM Mark Adams <mfadams at lbl.gov> wrote:

>
>
> On Thu, Jul 5, 2018 at 12:41 PM Tobin Isaac <tisaac at cc.gatech.edu> wrote:
>
>> On Thu, Jul 05, 2018 at 09:28:16AM -0400, Mark Adams 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. 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.)
>>
>> Out of curiosity, is the mesh immutable for a full simulation or adaptive?
>> If it's immutable, that seems like a poster child for the "private by
>> default, shared by choice" paradigm.
>>
>
> This is Chombo so it is dynamic.
>

We need more competitors like this :) We need to give more talks advocating
serial meshes,
unstable algorithms, OpenMP, and templates.

   Matt


>
>

>> > 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).
>>
>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
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