Host-to-Intel arria streaming over PCIe

To answer the original question, this feature is very useful for "out-of-core processing"; i.e. processing data that is too big to fit on the FPGA external memory but can fit on the host memory. There is a large body of work in HPC and Big Data using GPUs where overlapping/pipelining of compute and PCI-E transfer is implemented using double buffering on the GPU memory. For applications that can be "streamed", host channels on FPGAs can be used to efficiently implement out-of-core processing without the need for double-buffering. However, for applications that cannot be streamed, this feature is not applicable and double buffering will have to be used as is done on GPUs.