Dear Cristian,
as you probably know C class is one of the large classes for the NAS benchmarks. That is likely to mean that the application is taking much more time to do the actual computation rather than communication. This could explain why you see this little difference between the two execution: because communication is so little compared with the rest.
In order to validate this reasoning, you can profile or trace the application using some of the performance tools available out there (Vampir, Paraver, TAU, HPCToolkit, Scalasca,...) and see which how is the communication compared to the computation.
Regards. On 22/07/15 09:19, Crisitan RUIZ wrote:
Hello, I'm running OpenMPI 1.8.5 on a cluster with the following characteristics: Each node is equipped with two Intel Xeon E5-2630v3 processors (with 8 cores each), 128 GB of RAM and a 10 Gigabit Ethernet adapter. When I run the NAS benchmarks using 8 cores in the same machine, I'm getting almost the same performance as using 8 machines running a mpi process per machine. I used the following commands: for running multi-node: mpirun -np 8 --machinefile machine_file.txt --mca btl self,sm,tcp --allow-run-as-root mg.C.8 for running in with 8 cores: mpirun -np 8 --mca btl self,sm,tcp --allow-run-as-root mg.C.8 I got the following results: 8 cores: Mop/s total = 19368.43 8 machines: Mop/s total = 19326.60 The results are similar for other benchmarks. Is this behavior normal? I was expecting to see a better behavior using 8 cores given that they use directly the memory to communicate. Thank you, Cristian _______________________________________________ users mailing list us...@open-mpi.org Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users Link to this post: http://www.open-mpi.org/community/lists/users/2015/07/27295.php
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