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Subject: Re: [OMPI users] Hybrid program
From: Gabriele Fatigati (g.fatigati_at_[hidden])
Date: 2008-11-20 02:53:49


Is there a way to assign one thread to one core? Also from code, not
necessary with OpenMPI option.

Thanks.

2008/11/19 Stephen Wornom <stephen.wornom_at_[hidden]>:
> 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
>>>>
>>>
>>> _______________________________________________
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>>>
>>>
>>>
>>
>>
>>
>>
>
>
> --
> stephen.wornom_at_[hidden]
> 2004 route des lucioles - BP93
> Sophia Antipolis
> 06902 CEDEX
>
> Tel: 04 92 38 50 54
> Fax: 04 97 15 53 51
>
>
> _______________________________________________
> 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]