FLUENT 6.3.xx hangs when trying to use more than 4 processors on a multi-processor system
By default, FLUENT is using the SSM channel for MPICH2. SSM stands for Combined Socket and Shared memory Communication. Normally, this channel gives good performance if the computation is on a cluster composed of dual-processor and/or dual-core machines. However, if the user runs a FLUENT job on a big Shared Memory machine, for example, 8-cores, the performance of SSM has not been optimized for this purpose.
Resolution: Users may try the shared memory channel by setting the following environment variable before launching FLUENT:
Setting the MPICH2_CHANNEL Variable
1.Open up Control Panel, System, Advanced, Environment Variables.
2.Under User Variables or System Variables, click the New button.
3.In the Variable text box type: MPICH2_CHANNEL
4.In the Value text box type: shm
If this is set properly you should see the following printout in the FLUENT console
User defined: MPICH2_CHANNEL=shm