[petsc-dev] Question about MPICH device we use

[Matthew Knepley]

On Wed, Jul 22, 2020 at 2:34 PM Satish Balay <balay at mcs.anl.gov> wrote:

> BTW: Last we compared performance [many years ago] the difference was not
> a factor of 2 - but a few percentage points.
>
> Which petsc example can we re-run to compare?
>

Not sure. Scott I think was running his new MHD stuff. His post is on the
#general channel on the Firedrake slack.

  Thanks,

     Matt


> Satish
>
> On Wed, 22 Jul 2020, Satish Balay via petsc-dev wrote:
>
> > Primarily because ch3:sock performance does not degrade in oversubscribe
> mode - which is developer friendly - i.e on your laptop.
> >
> > And folks doing optimized runs should use a properly tuned MPI for their
> setup anyway.
> >
> > In this case --download-mpich-device=ch3:nemesis is likely appropriate
> if using --download-mpich [and not using a separate/optimized MPI]
> >
> > Having defaults that satisfy all use cases is not practical.
> >
> > Satish
> >
> > On Wed, 22 Jul 2020, Matthew Knepley wrote:
> >
> > > We default to ch3:sock. Scott MacLachlan just had a long thread on the
> > > Firedrake list where it ended up that reconfiguring using ch3:nemesis
> had a
> > > 2x performance boost on his 16-core proc, and noticeable effect on the
> 4
> > > core speedup.
> > >
> > > Why do we default to sock?
> > >
> > >   Thanks,
> > >
> > >      Matt
> > >
> > >
> >
>
>

-- 
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.cse.buffalo.edu/~knepley/>
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