[petsc-users] LU factorization and solution of independent matrices does not scale, why?

[Jed Brown]

On Fri, Dec 21, 2012 at 9:00 AM, Alexander Grayver
<agrayver at gfz-potsdam.de>wrote:

> > MUMPS uses MPI_Iprobe on MPI_COMM_WORLD (hard-coded).
>
> Any reason they do it that way? Which part of the code is that (i.e.
> analysis/factorization/**solution.)?
>

They should Iprobe on the proper communicator. I don't know if it's a
mistake in MUMPS or if they were working around a historical bug in some
MPI implementation. At this point, we don't have sufficiently detailed
profiling to determine that this has anything to do with the strange
performance degradation that Thomas is seeing.
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