[mpich-discuss] Oversubscription with Nemesis

[Jeff Hammond]

Hi Jed,

I don't see the problem.  You assert that people who oversubscribe
don't care about performance, and all that MPICH2 is doing wrong with
Nemesis right now has to do with performance, right?

Anyone who cares about performance shouldn't be relying upon PETSc to
build MPICH2, so I see no problem in PETSc continuing to build MPICH2
in a conservative way that supports oversubscription effectively.

Does the PETSc build system support options e.g.
--download-mpich=nemesis vs. --download-mpich=sockets?  That would
seem to resolve all of your issues with minimal effort.

Best,

Jeff

On Tue, Sep 11, 2012 at 2:11 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
> I know this has been filed as a ticket, but it seems to be postponed
> quasi-indefinitely at this point.
>
> http://trac.mcs.anl.gov/projects/mpich2/ticket/79
>
> I'd like to emphasize that over-subscription is extremely commonly used
> during initial development and method experimentation (not performance
> studies, obviously) and consequently, PETSc continues to use ch3:sock as the
> default for new installs (via --download-mpich, which is used by a large
> fraction of PETSc users). It appears that you are trying to wean the
> community off of sock in favor of nemesis, but as long as this bug is not
> fixed, you will continue to get thousands of new sock installs.
>
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-- 
Jeff Hammond
Argonne Leadership Computing Facility
University of Chicago Computation Institute
jhammond at alcf.anl.gov / (630) 252-5381
http://www.linkedin.com/in/jeffhammond
https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond