[OMPI users] custom sparse collective non-reproducible deadlock, MPI_Sendrecv, MPI_Isend/MPI_Irecv or MPI_Send/MPI_Recv question

Hi All, My MPI program's basic task consists of regularly establishing point-to-point communication with other procs via MPI_Alltoall, and then to communicate data. I tested it on two HPC clusters with 32-256 MPI tasks. One of the systems (HPC1) this custom collective runs flawlessly, while on

[OMPI users] Latency of 250 microseconds with Open-MPI 1.4.3, Mellanox Infiniband and 256 MPI ranks

Hello, Open-MPI 1.4.3 on Mellanox Infiniband hardware gives a latency of 250 microseconds with 256 MPI ranks on super-computer A (name is colosse). The same software gives a latency of 10 microseconds with MVAPICH2 and QLogic Infiniband hardware with 512 MPI ranks on super-computer B (name is g