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Subject: Re: [OMPI users] #cpus/socket
From: Peter Kjellström (cap_at_[hidden])
Date: 2011-09-13 06:59:08


On Tuesday, September 13, 2011 09:07:32 AM nn3003 wrote:
> 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.

In reality a 12 core Magnycours is two 6 core dies on a socket. I'm guessing
that the topology code sees your 4x 12 core as a 8x 6 core.

/Peter