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Subject: Re: [OMPI users] Hybrid program
From: Gabriele Fatigati (g.fatigati_at_[hidden])
Date: 2008-11-18 12:06:53


Hi,
how can i set "slot mapping" as you told me? With TASK GEOMETRY? Or is
a new 1.3 OpenMPI feature?

Thanks.

2008/11/18 Ralph Castain <rhc_at_[hidden]>:
> Unfortunately, paffinity doesn't know anything about assigning threads to
> cores. This is actually a behavior of Linux, which only allows paffinity to
> be set at the process level. So, when you set paffinity on a process, you
> bind all threads of that process to the specified core(s). You cannot
> specify that a thread be given a specific core.
>
> In this case, your two threads/process are sharing the same core and thus
> contending for it. As you'd expect in that situation, one thread gets the
> vast majority of the attention, while the other thread is mostly idle.
>
> If you can upgrade to the beta 1.3 release, try using the slot mapping to
> assign multiple cores to each process. This will ensure that the threads for
> that process have exclusive access to those cores, but will not bind a
> particular thread to one core - the threads can "move around" across the
> specified set of cores. Your threads will then be able to run without
> interfering with each other.
>
> Ralph
>
>
> On Nov 18, 2008, at 9:18 AM, Gabriele Fatigati wrote:
>
>> Dear OpenMPI developers,
>> i have a strange problem with mixed program MPI+OPENMP over OpenMPI
>> 1.2.6. I'm using PJL TASK GEOMETRY in LSF Scheduler, setting 2 MPI
>> process every compute node, and 2 OMP threads per process. Using
>> paffinity and maffinity, i've noted that over every node, i have 2
>> thread that works 100%, and 2 threads doesn't works, or works very
>> few.
>>
>> If i disable paffinity and maffinity, 4 threads works well, without
>> load imbalance.
>> I don't understand this issue: paffinity and maffinity should map
>> every thread over a specific core, optimizing the cache flow, but i
>> have this without settings there!
>>
>> Can i use paffinity and maffinity in mixed MPI+OpenMP program? Or it
>> works only over MPI thread?
>>
>> Thanks in advance.
>>
>>
>> --
>> Ing. Gabriele Fatigati
>>
>> CINECA Systems & Tecnologies Department
>>
>> Supercomputing Group
>>
>> Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy
>>
>> www.cineca.it Tel: +39 051 6171722
>>
>> g.fatigati_at_[hidden]
>> _______________________________________________
>> users mailing list
>> users_at_[hidden]
>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>
> _______________________________________________
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> users_at_[hidden]
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>
>

-- 
Ing. Gabriele Fatigati
CINECA Systems & Tecnologies Department
Supercomputing  Group
Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy
www.cineca.it                    Tel:   +39 051 6171722
g.fatigati_at_[hidden]