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Subject: [OMPI users] #cpus/socket
From: nn3003 (nn3003_at_[hidden])
Date: 2011-09-13 03:07:32

Hello !
I am running wrf model on 4x AMD 6172 which is 12 core CPU. I use OpenMPI 1.4.3 and libgomp 4.3.4. I have binaries compiled for shared-memory and distributed-memory (OpenMP and OpenMPI)
I use following command
mpirun -np 4 --cpus-per-proc 6 --report-bindings --bysocket wrf.exe
It works ok and in top i see there are 4 wrf.exe and each has 6 threads on cpu0-5 12-17 24-29 36-41
However, if I want to run 8 or more e.g.
mpirun -np 4 --cpus-per-proc 12 --report-bindings --bysocket wrf.exe
I get error
Your job has requested more cpus per process(rank) than there
are cpus in a socket:
  Cpus/rank: 8
  #cpus/socket: 6
Why is that ? There are 12 cores per socket in AMD 6172.
Thank you for help !