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

[Mark Adams]

I don't need your branch because 1) we are not doing any communication in
this VecAssembly and I added the IGNORE stuff just to make sure and 2) we
are catching load imbalance from another part of the code, I am now sure.
I can now see that VecAssemblyBegin's timers do not report this type of
load imbalance because it starts with a synch.  This is what I suspected
but I was wondering why the timers did not report this load imbalance.

On Fri, May 29, 2015 at 11:12 AM, Jed Brown <jed at jedbrown.org> wrote:

> 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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