Bug#850229: dune-grid: FTBFS (not enough slots available)

[Ansgar Burchardt]

Control: reassign -1 openmpi-bin 2.0.2~git.20161225-8
Control: severity -1 important
Control: retitle -1 openmpi-bin: default for oversubscription changed

Santiago Vila writes:
> Package: src:dune-grid
> Version: 2.5.0-1
> Severity: serious
>
> Dear maintainer:
>
> I tried to build this package in stretch with "dpkg-buildpackage -A"
> (which is what the "Arch: all" autobuilder would do to build it)
> but it failed:
[...]
> Status:    FAILED
> Output:
>            --------------------------------------------------------------------------
>            There are not enough slots available in the system to satisfy the 2 slots
>            that were requested by the application:
>              test-yaspgrid-yaspfactory-1d
>            
>            Either request fewer slots for your application, or make more slots available
>            for use.
>            --------------------------------------------------------------------------

This looks like OpenMPI changed its default for oversubscription: it
seems to now default to not allowing starting more processes than cores
available (cores, not threads even).  The man page still documents the
`--nooversubscribe` option, though `mpirun --help` shows a
`--oversubscribe` option (which is not understood by older versions).

Other implementations of `mpirun` (mpich) don't seem to understand this
option either, but seem to allow oversubscription by default (like older
versions of OpenMPI).  So one cannot pass the new option to `mpirun`
unconditionally.

I think it is a bug in OpenMPI to just change this default; at least
there should be a way to control this via an environment variable so one
doesn't have to provide OpenMPI-specific options to `mpirun`.

Ansgar