[petsc-dev] [petsc-maint] running CUDA on SUMMIT

[Mark Adams]

On Wed, Aug 14, 2019 at 3:37 PM Jed Brown <jed at jedbrown.org> wrote:

> Mark Adams via petsc-dev <petsc-dev at mcs.anl.gov> writes:
>
> > On Wed, Aug 14, 2019 at 2:35 PM Smith, Barry F. <bsmith at mcs.anl.gov>
> wrote:
> >
> >>
> >>   Mark,
> >>
> >>    Would you be able to make one run using single precision? Just single
> >> everywhere since that is all we support currently?
> >>
> >>
> > Experience in engineering at least is single does not work for FE
> > elasticity. I have tried it many years ago and have heard this from
> others.
> > This problem is pretty simple other than using Q2. I suppose I could try
> > it, but just be aware the FE people might say that single sucks.
>
> When they say that single sucks, is it for the definition of the
> operator or the preconditioner?
>

Operator.

And "ve seen GMRES stagnate when using single in communication in parallel
Gauss-Seidel. Roundoff is nonlinear.


>
> As point of reference, we can apply Q2 elasticity operators in double
> precision at nearly a billion dofs/second per GPU.


> I'm skeptical of big wins in preconditioning (especially setup) due to
> the cost and irregularity of indexing being large compared to the
> bandwidth cost of the floating point values.
>
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