[Pkg-openmpi-maintainers] Bug#849974: openmpi: not enough slots available

[Thibaut Paumard]

Dear Heinrich,

I also had noted this change in behaviour, I don't know whether this is
intentional. It looks like openmpi does not want to do oversubscription
by default anymore. You can get the old behaviour back by using the
--map-by option:

mpirun --map-by socket:OVERSUBSCRIBE -np 4 python -c "print 'hello'"



Le 02/01/2017 à 20:37, Heinrich Schuchardt a écrit :
> I am running on Intel Core i5-6300U CPU @ 2.40GHz.
> /proc/cpuinfo reports 4 CPUs.

http://ark.intel.com/fr/products/88190/Intel-Core-i5-6300U-Processor-3M-Cache-up-to-3_00-GHz

Your CPU has 4 threads, but only 2 real cores. So the real limit for
oversubscription is 2 rather than 4.

> mpirun -np 2 --hostfile hostfile python -c "print 'hello'"
> works fine.
> 
> mpirun -np 4 --hostfile hostfile python -c "print 'hello'"
> fails with
> "There are not enough slots available in the system to satisfy the 4 slots"
> 
> https://www.open-mpi.org/faq/?category=running#slots-without-hostfiles
> describes that overprovisioning should work
> 
> Best regards
> 
> Heinrich Schuchardt

Kind regards, Thibaut