[mpich-discuss] A general question to the community on data sharing for multi core nodes

[Dave Goodell]

On Aug 25, 2010, at 3:17 AM CDT, Pascal Deveze wrote:

> If I understand, you have 2 sockets (i7) of 4 cores each. Your nodes are NUMA. Do you place your processes and threads ?
> 
> If you do not place your processes, they will migrate from one socket to the other. That could be the contention you observed.
> I suggest you to use 2 MPI processes per node and place each on one socket by the command taskset (Linux).

If you are using hydra, you don't need to bother with "taskset" to pin your processes: http://wiki.mcs.anl.gov/mpich2/index.php/Using_the_Hydra_Process_Manager#Process-core_Binding

Just use one of the binding options instead.

-Dave