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Subject: Re: [hwloc-users] hwloc set membind function
From: Gabriele Fatigati (g.fatigati_at_[hidden])
Date: 2011-09-25 14:57:48


My goal is to set memory binding policy for future allocations for each
thread.

So, according to definition of set_membind function:

"Set the default memory binding policy of the current process or thread to
prefer the
NUMA node(s) near the specified cpuset."

and according to definition of HWLOC_MEMBIND_BIND flag:

"Allocate memory on the specified nodes."

Merging togheter, I expect to set memory policy of thread/process equal to
allocate memory on local node. But in my example,

after done this, memory is allocated not in a local node of thread that does
set_membind and malloc, but in node of thread that touches it. And I don't
understand this behaviour :(

2011/9/25 Brice Goglin <Brice.Goglin_at_[hidden]>

> **
> Le 25/09/2011 20:27, Gabriele Fatigati a écrit :
>
> if(tid==0){
>
> set_membind(HWLOCMEMBIND_BIND, node 0)
> malloc(array)...
>
> }
>
> if (tid==1){
> set_membind(HWLOCMEMBIND_BIND, node 1)
>
> for(i...)
> array(i)
> }
>
> end parallel region
>
>
> array is allocated on node 1, not node 0 as I expected So it seems
> set_membind() of second thread influence in some manner array allocation
> using first touch.
>
>
> Why do you call set_membind() here? It's whole point is to change the
> allocation policy of the current thread. If this thread then first-touches
> some data, this data will obviously get allocated acocording to
> set_membind().
>
> If you don't want set_membind() to modify the allocation policy of the
> current thread, why do you call it?
>
> 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