[OMPI users] --oversubscribe option

[Gilles Gouaillardet]

Mahmoud,

By default 1 slot = 1 core, that is why you need —oversubscribe or
—use-hwthread-cpus to run 16 MPI tasks.

It seems your lammps job benefits from hyper threading. Some applications
behave like this, and this is not odd a priori.

Cheers,

Gilles

I’m not entirely sure what you are asking here. If you use oversubscribe,
we do not bind your processes and you suffer some performance penalty for
it. If you want to run one process/thread and retain binding, then do not
use --oversubscribe and instead use --use-hwthread-cpus
Hi,
On a Ryzen 1800x which has 8 cores and 16 threads, when I run "mpirun -np
16 lammps..." I get an error that there is not enough slot. It seems that
--oversubscribe option will fix that.
Odd thing is that when I run "mpirun -np 8 lammps" it takes about 46
minutes to complete the job while with "mpirun --oversubscribe -np 16
lammps" it takes about 39 minutes.
I want to be sure that I "-np 16" uses are logical cores. Is that
confirmed with --oversubscribe?
Regards,
Mahmood
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