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Subject: Re: [OMPI users] Hybrid program
From: Stephen Wornom (stephen.wornom_at_[hidden])
Date: 2008-11-19 03:32:17


Gabriele Fatigati wrote:
> Ok,
> but in Ompi 1.3 how can i enable it?
>
This may not be relevant, but I could not get a hybrid mpi+OpenMP code
to work correctly.
Would my problem be related to Gabriele's and perhaps fixed in openmpi 1.3?
Stephen
> 2008/11/18 Ralph Castain <rhc_at_[hidden]>:
>
>> I am afraid it is only available in 1.3 - we didn't backport it to the 1.2
>> series
>>
>>
>> On Nov 18, 2008, at 10:06 AM, Gabriele Fatigati wrote:
>>
>>
>>> 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
>>>>>
>>>> _______________________________________________
>>>> users mailing list
>>>> users_at_[hidden]
>>>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>>>
>>>>
>>>>
>>>
>>> --
>>> 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
>>>
>> _______________________________________________
>> users mailing list
>> users_at_[hidden]
>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>
>>
>>
>
>
>
>

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