Hmmm…you mean for procs on the same node? I’m not sure how you can do it
without introducing another data exchange, and that would require the app to
execute it since otherwise we have no idea when they set the affinity.
If we assume they set the affinity prior to calling MPI_Init, then we could do
it - but at the cost of forcing a modex. You can only detect your own affinity,
so to get the relative placement, you have to do an exchange if we can’t pass
it to you. Perhaps we could offer it as an option?
> On Apr 26, 2016, at 2:27 PM, Sylvain Jeaugey <sjeau...@nvidia.com> wrote:
>
> Within the BTL code (and surely elsewhere), we can use those convenient
> OPAL_PROC_ON_LOCAL_{NODE,SOCKET, ...} macros to figure out where another
> endpoint is located compared to us.
>
> The problem is that it only works when ORTE defines it. The NODE works almost
> always since ORTE is always doing it. But for the NUMA, SOCKET, or CORE to
> work, we need to use Open MPI binding/mapping capabilities. If the process
> affinity was set with something else (custom scripts using taskset, cpusets,
> ...), it doesn't work.
>
> How hard do you think it would it be to detect the affinity and set those
> flags using hwloc to figure out if we're on the same {SOCKET, CORE, ...} ?
> Where would it be simpler to do this ?
>
> Thanks.
> Sylvain
>
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