Re: [OMPI users] Hybrid program

[Edgar Gabriel]

if you look at recent versions of libnuma, there are two functions 
called numa_run_on_node() and numa_run_on_node_mask(), which allow 
thread-based assignments to CPUs....

Thanks
Edgar
Gabriele Fatigati wrote:
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.wor...@sophia.inria.fr>:
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 <r...@lanl.gov>:

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 <r...@lanl.gov>:

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.fatig...@cineca.it
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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.fatig...@cineca.it
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--
stephen.wor...@sophia.inria.fr
2004 route des lucioles - BP93
Sophia Antipolis
06902 CEDEX

Tel: 04 92 38 50 54
Fax: 04 97 15 53 51


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