Hi, I have encountered really bad performance when all the nodes send data to all the other nodes. I use Isend and Irecv with multiple outstanding sends per node. I debugged the behavior and came to the following conclusion: It seems that one sender locks out all other senders for one receiver. This sender releases the receiver only when there are no more sends posted or a node with lower rank, wants to send to this node (deadlock prevention). As a consequence, node 0 sends all its data to all nodes, while all others are waiting, then node 1 sends all the data, …
What is the rationale behind this behaviour and can I change it by some MCA parameter? Thanks Stephan
