Artur Tyliszczak ha scritto:
> Dear All,
>
> We have 8 dual cores Opterons 8214HE cluster (total: 32 cores).
> If I run a job using mpirun (mpirun -np 4 ./jobname) how can I know
> whether my job is running on 2 physical processors (4 cores) or
> separate 4 processors (also 4 cores but from different processors)?
>
> Is is there any way to chose one of the above option by some mpirun options?
> What is more efficient: 2 cores on 2 processors OR 4 cores on 4 separate
> processors?
>
> Thank you in advance.
> Artur T.
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> This list is archived at http://www.lam-mpi.org/MailArchives/lam/
>
Hi Artur
As it has already been pointed out in this list, if you have a plain SMP
system you should not worry much about on which socket/core your
parallel processes run within a single node, provided you have a recent
enough kernel (multicore/hyperthread aware) it will probably do a good
scheduling job.
Concerning the way to spread multiple processes on different nodes, it
may surely depend on the application, I would add to Tim's answer that I
saw some benchmarks where the same MPI application (whose performance
bottlencks are memory access and communication) had the following
behavior (supposing to have dual processor*dual core nodes):
on Opteron systems maximum performance was obtained with 4 MPI processes
per node, thus using all the cores =>communication bottleneck
on Xeon systems the maxiumum performance was reached using double number
of nodes but starting only 2 processes per node, even if some other
process were running on the same nodes =>memory access bottleneck
best regards, Davide
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