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.
> On Jan 10, 2018, at 10:48 AM, r...@open-mpi.org wrote:
>
> Set the MCA param “rmaps_base_oversubscribe=1” in your default MCA param
> file, or in your environment
>
>> On Jan 10, 2018, at 4:42 AM, Florian Lindner wrote:
>>
>> 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
jsquy...@cisco.com
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