Ben Smith has launched the new HPC-Opinion blog with a look at the differences between Nvidia GPUDirect version 1 and GPUDirect version 2.
GPUDirect version 1 enables better communication between remote GPUs over InfiniBand. Why InfiniBand? Because you need to use RDMA for the data communications between the GPUs, else it does not work. Without RDMA support, you will require the server CPU to be involved in the data path, hence no much of “GPUDirect”… Looking into the InfiniBand vendors – the one that has RDMA support is Mellanox, and the one that does not (well, they have kind of software emulation of RDMA) is QLogic. No surprise why NVIDIA announced the GPUDirect project with Mellanox.