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

[Jed Brown]

Mark Adams <mfadams at lbl.gov> writes:

> Thanks, this code does not have any communication in VecAssembly so I added
> the INGNORE stuff and added a barrier before this section of code.  I am
> suspecting that VecAssembly is catching load imbalance but not reporting it
> for some reason.

If you put a barrier before, it starts at about the same time on all
processes.  The operation contains synchronization followed by
(scalable) point-to-point messaging.  The slowness is almost certainly
caused by the non-scalable algorithm -- I've seen it with other
applications.  So try my branch.
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