[OMPI users] Setting mpirun default parameters in a file

[Florian Lindner]

Hello,

a recent openmpi update on my Arch machine seems to have enabled --nooversubscribe, as described in the manpage. Since I
regularly test on my laptop with just 2 physical cores, I want to set --oversubscribe by default.

How can I do that?

I am also a bit surprised, that openmpi takes the physical number of cores into account, not the logical (which is 4 on
my machine).

Thanks,
Florian

[r***@open-mpi.org]

Set the MCA param “rmaps_base_oversubscribe=1” in your default MCA param file, or in your environment

Post by Florian Lindner
Hello,
a recent openmpi update on my Arch machine seems to have enabled --nooversubscribe, as described in the manpage. Since I
regularly test on my laptop with just 2 physical cores, I want to set --oversubscribe by default.
How can I do that?
I am also a bit surprised, that openmpi takes the physical number of cores into account, not the logical (which is 4 on
my machine).
Thanks,
Florian
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https://lists.open-mpi.org/mailman/listinfo/users

[Jeff Squyres (jsquyres)]

See https://www.open-mpi.org/faq/?category=tuning#setting-mca-params for a little more info on how to set MCA params.

In terms of physical vs. logical -- are you talking about hyperthreading?

If so, Open MPI uses the number of *cores* (by default), because that's what "most" HPC users want (I put "most" in quotes because this can quickly turn into a religious debate -- the "cores vs. hyperthreads" discussion has come up on this list a few times over the years, and "most" HPC-related workloads still tend to benefit from using a whole core vs. a hyperthread).

Regardless, you can have Open MPI use hyperthreads by default (instead of cores) with the mpirun option --use-hwthread-cpus.

Post by r***@open-mpi.org
Set the MCA param “rmaps_base_oversubscribe=1” in your default MCA param file, or in your environment

Post by Florian Lindner
Hello,
a recent openmpi update on my Arch machine seems to have enabled --nooversubscribe, as described in the manpage. Since I
regularly test on my laptop with just 2 physical cores, I want to set --oversubscribe by default.
How can I do that?
I am also a bit surprised, that openmpi takes the physical number of cores into account, not the logical (which is 4 on
my machine).
Thanks,
Florian
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--
Jeff Squyres
***@cisco.com

[Florian Lindner]

Post by Jeff Squyres (jsquyres)
See https://www.open-mpi.org/faq/?category=tuning#setting-mca-params for a little more info on how to set MCA params.

Thanks!

Post by Jeff Squyres (jsquyres)
In terms of physical vs. logical -- are you talking about hyperthreading?

Yes.

Post by Jeff Squyres (jsquyres)
If so, Open MPI uses the number of *cores* (by default), because that's what "most" HPC users want (I put "most" in quotes because this can quickly turn into a religious debate -- the "cores vs. hyperthreads" discussion has come up on this list a few times over the years, and "most" HPC-related workloads still tend to benefit from using a whole core vs. a hyperthread).

Not wanting to open that debate again ;-). I was just surprised because most applications take the logical
(hyperthreading) number of CPUs.

Best,
Florian

Post by Jeff Squyres (jsquyres)
Regardless, you can have Open MPI use hyperthreads by default (instead of cores) with the mpirun option --use-hwthread-cpus.

Post by r***@open-mpi.org
Set the MCA param “rmaps_base_oversubscribe=1” in your default MCA param file, or in your environment

Post by Florian Lindner
Hello,
a recent openmpi update on my Arch machine seems to have enabled --nooversubscribe, as described in the manpage. Since I
regularly test on my laptop with just 2 physical cores, I want to set --oversubscribe by default.
How can I do that?
I am also a bit surprised, that openmpi takes the physical number of cores into account, not the logical (which is 4 on
my machine).
Thanks,
Florian
_______________________________________________
users mailing list
https://lists.open-mpi.org/mailman/listinfo/users

_______________________________________________
users mailing list
https://lists.open-mpi.org/mailman/listinfo/users