[petsc-dev] Soliciting suggestions for linear solver work under SciDAC 4 Institutes

Matthew Knepley knepley at gmail.com
Thu Jul 7 20:35:59 CDT 2016

On Thu, Jul 7, 2016 at 8:03 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

> > On Jul 7, 2016, at 7:05 PM, Jeff Hammond <jeff.science at gmail.com> wrote:
> >
> >
> >
> > On Thu, Jul 7, 2016 at 1:04 PM, Matthew Knepley <knepley at gmail.com>
> wrote:
> > On Fri, Jul 1, 2016 at 4:32 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> >    The DOE SciDAC institutes have supported PETSc linear solver
> research/code development for the past fifteen years.
> >
> >     This email is to solicit ideas for linear solver research/code
> development work for the next round of SciDAC institutes (which will be a 4
> year period) in PETSc. Please send me any ideas, no matter how crazy, on
> things you feel are missing, broken, or incomplete in PETSc with regard to
> linear solvers that we should propose to work on. In particular, issues
> coming from particular classes of applications would be good. Generic
> "multi physics" coupling types of things are too general (and old :-))
> while  work for extreme large scale is also out since that is covered under
> another call (ECP). But particular types of optimizations etc for existing
> or new codes could be in, just not for the very large scale.
> >
> >     Rough ideas and pointers to publications are all useful. There is an
> extremely short fuse so the sooner the better,
> >
> > I think the suggestions so far are fine, however they all seem to start
> at the "how", whereas I would prefer we start at the "why". Maybe something
> like
> >
> > 1) How do we run at bandwidth peak on new architectures like Cori or
> Aurora?
>   Huh, there is a how here, not a why?

The why is "We need to run at bandwidth peak on new arches". I do not
prescribe the How, just ask for it.


> >
> > Patrick and Rich have good suggestions here. Karl and Rich showed some
> promising numbers for KNL at the PETSc meeting.
> >
> >
> > Future systems from multiple vendors basically move from 2-tier memory
> hierarchy of shared LLC and DRAM to a 3-tier hierarchy of fast memory (e.g.
> HBM), regular memory (e.g. DRAM), and slow (likely nonvolatile) memory  on
> a node.
>   Jeff,
>    Would Intel sell me a system that had essentially no regular memory
> DRAM (which is too slow anyway) and no slow memory (which is absurdly too
> slow)?  What cost savings would I get in $ and power usage compared to say
> what is going in the theta? 10% and 20%, 5% and 30%, 5% and 5 %? If it is a
> significant savings then get the cut down machine, if it is insignificant
> than realize the cost of not using it (the DRAM you paid so little for) is
> insignificant and not worth worrying about, just like cruise control when
> you don't use the highway. Actually I could use the DRAM to store the
> history needed for the adjoints; so maybe it is ok to keep, but surely not
> useful for data that is continuously involved in the computation.
>    Barry
> > Xeon Phi and some GPUs have caches, but it is unclear to me if it
> actually benefits software like PETSc to consider them.  Figuring out how
> to run PETSc effectively on KNL should be generally useful...
> >
> > Jeff
> >
> > --
> > Jeff Hammond
> > jeff.science at gmail.com
> > http://jeffhammond.github.io/

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
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