[mpich-devel] MPI_Recv, blocking call concept

Lisandro Dalcin dalcinl at gmail.com
Fri Jun 8 06:17:57 CDT 2018

On Fri, 8 Jun 2018 at 03:18, Jed Brown <jed at jedbrown.org> wrote:
> Jeff Hammond <jeff.science at gmail.com> writes:
> > The PETSc folks appear to be the biggest proponents of blocking poll
> > (solely for purposes of running dozens of MPI processes on their
> > laptops, it seems) and they seem to prefer ch3:sock.  I defer to their
> > experience as to whether a better implementation exists.
> Indeed, the test suite has several tests that use 9-16 ranks and take
> less than 1 second even when oversubscribed using ch3:sock, but are
> disturbingly slow with modern MPICH.  The conundrum of developers not
> being able to debug tests on their laptop and many CI solutions not
> being able to execute those tests is reminiscent of the testing fiasco
> that is multi-GPU development.

Intel MPI seems to have some backoff support with I_MPI_SPIN_COUNT,
I_MPI_SHM_SPIN_COUNT, and some others vars. I never tested how well
these features work, though.

I guess PETSc developers would just like to have a way to somehow
alter behavior at runtime by exporting some environ vars in a CI
script. This would benefit testing and latency-insensitive use cases.

Lisandro Dalcin
Research Scientist
Computer, Electrical and Mathematical Sciences & Engineering (CEMSE)
Extreme Computing Research Center (ECRC)
King Abdullah University of Science and Technology (KAUST)

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