my bad, I was assuming KMP_AFFINITY was used
so let me put it this way :
do *not* use KMP_AFFINITY with mpirun -bind-to none, otherwise, you will
very likely end up doing time sharing ...
Cheers,
Gilles
On 6/22/2016 5:07 PM, Jeff Hammond wrote:
Linux should not put more than one thread on a core if there are free
cores. Depending on cache/bandwidth needs, it may or may not be
better to colocate on the same socket.
KMP_AFFINITY will pin the OpenMP threads. This is often important for
MKL performance. See https://software.intel.com/en-us/node/522691 for
details.
Jeff
On Wed, Jun 22, 2016 at 9:47 AM, Gilles Gouaillardet
<gil...@rist.or.jp <mailto:gil...@rist.or.jp>> wrote:
Remi,
Keep in mind this is still suboptimal.
if you run 2 tasks per node, there is a risks threads from
different ranks end up bound to the same core, which means time
sharing and a drop in performance.
Cheers,
Gilles
On 6/22/2016 4:45 PM, remi marchal wrote:
Dear Gilles,
Thanks a lot.
The mpirun --bind-to-none solve the problem.
Thanks a lot,
Regards,
Rémi
Le 22 juin 2016 à 09:34, Gilles Gouaillardet <gil...@rist.or.jp
<mailto:gil...@rist.or.jp>> a écrit :
Remi,
in the same environment, can you
mpirun -np 1 grep Cpus_allowed_list /proc/self/status
it is likely Open MPI allows only one core, and in this case, i
suspect MKL refuses to do some time sharing and hence
transparently reduce the number of threads to 1.
/* unless it *does* time sharing, and you observed 4 threads
with the performance of one */
mpirun --bind-to none ...
will tell Open MPI *not* to bind on one core, and that should
help a bit.
note this is suboptimal, you should really ask mpirun to
allocate 4 cores per task, but i cannot remember the correct
command line for that
Cheers,
Gilles
On 6/22/2016 4:17 PM, remi marchal wrote:
Dear openmpi users,
Today, I faced a strange problem.
I am compiling a quantum chemistry software (CASTEP-16) using
intel16, mkl threaded libraries and openmpi-18.1.
The compilation works fine.
When I ask for MKL_NUM_THREAD=4 and call the program in serial
mode (without mpirun), it works perfectly and use 4 threads.
However, when I start the program with mpirun, even with 1 mpi
process, the program ran but only with 1 thread.
I never add such kind of trouble.
Does anyone have an explanation.
Regards,
Rémi
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