[petsc-dev] new P^1.5 algorithm in VecAssembleBegin?

Mark Adams mfadams at lbl.gov
Fri May 29 10:42:02 CDT 2015

On Fri, May 29, 2015 at 11:32 AM, Jed Brown <jed at jedbrown.org> wrote:

> Mark Adams <mfadams at lbl.gov> writes:
> > I don't need your branch because 1) we are not doing any communication in
> > this VecAssembly
> There is still synchronization cost in determining that nothing needs to
> be done.

I added:


Doesn't this remove the synchronization?

> Moreover, using a size P MPI_Allreduce for that (in
> PetscMaxSum) is non-scalable.  My branch uses MPI_Reduce_scatter_block
> (scalable) when available (MPI-2.2).
> > and I added the IGNORE stuff
> So it takes no time now and everything is groovy?
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