[stephen272]

I wouldn't say GPUs are killing off MPI. You still need some way to pass data between nodes/GPUs (most of these datasets can't fit within a single GPU). What you are seeing though, is less and less use of the CPU. If code developers decide to use GPUs, they try and move their data onto the GPU and keep it there for as long as possible (data movement across PCIe is a killer for performance). ORNL's new machine Sumiit [1] will have 1/4 the nodes of their current machine, Titan, but multiple GPUs per node. Thus emphasizing the move away from CPUs and onto GPUs. Again though, there are still 3K nodes and you need some efficient way to pass data between those nodes.

[1] https://www.olcf.ornl.gov/summit/