1. In a first processing node of a distributed data processing system having multiple processing nodes executing threads of a parallel job, a method for efficient inter-node communication among threads of the parallel job comprising: generating at the first processing node one or more messages for transmission to at least one other processing node accessible via a network, wherein the one or more messages are generated by/for a first thread executing at the first processing node and the at least one other processing node executes one or more second threads of a same parallel job as the first thread; and transmitting via a host fabric interface (HFI) the one or more messages via a one-to-all broadcast on the network, wherein the one or more messages are transmitted to a cluster of processing nodes across the network that execute threads of the same parallel job as the first thread.