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Subject: Re: [OMPI users] Hybrid OpenMPI / OpenMP run pins OpenMP threads to a single core
From: David Akin (nospamou_at_[hidden])
Date: 2010-08-10 16:49:19


Solved: The process to core locking was due to affinity being set at
the PSM layer. So I added -x IPATH_NO_CPUAFFINITY=1 to the mpirun
command.

Dave

On Wed, Aug 4, 2010 at 12:13 PM, Eugene Loh <eugene.loh_at_[hidden]> wrote:
>
> David Akin wrote:
>
>> All,
>> I'm trying to get the OpenMP portion of the code below to run
>> multicore on a couple of 8 core nodes.
>>
>
> I was gone last week and am trying to catch up on e-mail.  This thread was a little intriguing.
>
> I agree with Ralph and Terry:
>
> *) OMPI should not be binding by default.
> *) There is nothing in your program that would induce binding nor anything in your reported output that indicates binding is occurring.
>
> So, any possibility that your use of taskset or top is misleading?  Did you ever try running with --report-bindings as Terry suggested?
>
> The thread also discussed OMPI's inability to control the binding behavior of individual threads.  You can't manage individual threads with OMPI;  you'd have to use a thread-specific mechanism, and many OMP implementations support such mechanisms.  The best you could do with OMPI would be to unbind or bind broadly (e.g., to an entire socket), and that policy would be applied to all the threads within the process.
>
> But, all that should be unnecessary... there shouldn't be any binding by default in the first place.  I'd check into whether these threads really are being bound and, if so, why.
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