Slowdown p2p MPI calls

Dear MPi users,

I'm using IntelMPI cs-2011. My code (OpenMP + MPI)  does for each time step some send and receive MPI calls after a kernel computation. MPI calls are used for ghost cell exchange. (few kbytes)

I've noted a significative slowdown during the computation. I suppose the problem is in some low level MPI setting because by using OpenMPI that problem disappear. I'm using Inifiniband and 12 cores on 1 node, so just intranode communication is used.

I disabled shared memory inside a node, used dapl for intranode, decreased I_MPI_INTRANODE_THRESHOLD, set I_MPI_DAPL_TRANSLATION_CACHE to 0, without any good improvement. 

Do you have an idea because the p2p calls slowdown in running?

Thanks a lot.