[mpich-discuss] mpich collectives topology aware?

[Filip Blagojevic]

Hi,

Could anyone tell me if MPI_Allreduce() (and other collectives) is  
topology aware?
More specifically, I would like to know if MPI_Allreduce() will first  
perform a local reduction (within a single shared memory node), and  
then only one MPI rank will be chosen on each node to perform inter- 
node reduction. Or maybe the reduction is not aware of what MPI  
processes are sharing a node?

Thank you,
Filip