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

[Ansgar Burchardt]

On Thu, 2017-01-05 at 12:59 +0200, Graham Inggs wrote:
> On 05/01/2017 12:05, Santiago Vila wrote:
> > 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.
> >            ------------------------------------------------------
> > --------------------
> 
> I started seeing similar errors in other MPI applications since the 
> upload of openmpi 2.0.2~ to unstable.
> 
> The solution was to add --oversubscribe to the mpirun command line, 

Yes, it looks like OpenMPI changed the default :-/

> The bug should be reproducible with sbuild on a single CPU virtual
> > machine.
> > It always fail for me (I tried 10 times in different autobuilders).
> 
> If I understand correctly, --oversubscribe should be needed in your
> case where you have fewer CPUs than the number of processes
> requested, but I was seeing the errors even when there were more than
> enough CPUs available.

On my laptop with 4 cores + HT (so 8 threads), I see `mpirun` complain
once I start more than 4 processes, i.e. more processes than real
cores.  Did you count threads or cores when you tried?

Ansgar