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Subject: Re: [hwloc-users] hwloc set membind function
From: Gabriele Fatigati (g.fatigati_at_[hidden])
Date: 2011-09-25 06:45:52


2011/9/25 Gabriele Fatigati <g.fatigati_at_[hidden]>

>
>> * doing two set_area_membind on the same entire array is useless, the
> second one will overwrite the first one.
>
> But set_area_membind is for memory in general, not for a particular malloc.
> ( Is it rigth?)
>

> set_membind done by thread 2 has no reference with malloc(array) done by
> first thread.
>
>
> 2011/9/25 Brice Goglin <Brice.Goglin_at_[hidden]>
>
>> **
>> Le 25/09/2011 12:19, Gabriele Fatigati a écrit :
>>
>> Hi Brice,
>>
>> >The flag says "when the first touch occurs and the physical memory is
>> allocated for real, don't allocate on the local node (default), but >rather
>> allocate where specified by set_membind".
>>
>> If is it already allocated for real, how set_membind() can allocate on
>> other node?
>>
>>
>> Add the MIGRATE flag.
>>
>>
>> So, what's the difference between HWLOC_MEMBIND_BIND and
>> HWLOC_MEMBIND_FIRSTTOUCH?
>>
>>
>> First touch makes the allocation on the node local to the thread that
>> touches first (default on Linux).
>> BIND makes the allocation on the node specified in set_membind.
>>
>>
>> Doing the follow test:
>>
>> omp parallel region
>>
>> if(tid==0){
>> malloc(array)...
>> set_area_membind(HWLOCMEMBIND_BIND, node 0)
>> }
>>
>> if (tid==1){
>> set_area_membind(HWLOCMEMBIND_BIND, node 1)
>>
>>
>> If both set_area_membind work on the same array (not on different halves),
>> this is doubly-wrong:
>> * you have no guarantee that thread 0 has already finished doing the
>> malloc before thread 1 does set_area_membind on the buffer.
>> * doing two set_area_membind on the same entire array is useless, the
>> second one will overwrite the first one.
>>
>> Brice
>>
>>
>> _______________________________________________
>> hwloc-users mailing list
>> hwloc-users_at_[hidden]
>> http://www.open-mpi.org/mailman/listinfo.cgi/hwloc-users
>>
>
>
>
> --
> Ing. Gabriele Fatigati
>
> HPC specialist
>
> SuperComputing Applications and Innovation Department
>
> Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy
>
> www.cineca.it Tel: +39 051 6171722
>
> g.fatigati [AT] cineca.it
>

-- 
Ing. Gabriele Fatigati
HPC specialist
SuperComputing Applications and Innovation Department
Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy
www.cineca.it                    Tel:   +39 051 6171722
g.fatigati [AT] cineca.it