Currently SPDK consists of a usermode NVMe (PCIe-attached SSD) driver. We will soon be releasing a usermode driver for the Intel I/OAT DMA engine (copy offload hardware) that is available on some server platforms.
And can this be combined with PCIe-attached accelerators (e.g. Xeon Phi or GPUs)?
I am not familiar enough with the Xeon Phi or GPU programming model to say for sure, but they could possibly be used to offload tasks like hashing/dedup or other storage-related functions.
Sorry, I was not referring to accelerating storage-related functions, I was wondering about efficient DMA copy from one PCIe device (Intel NVM storage) to another (Xeon Phi accelerator) which would be for useful many different functions, if the NVM storage device capacity is much larger than the accelerator device memory.
Some of the straightforward use cases would be inside network-attached storage appliances (ideally in conjunction with a user-mode network stack) or in a database (database systems already typically want to avoid any OS interference with storage access). In general, the NVMe driver can be dropped in fairly easily when existing code is using something like Linux AIO with O_DIRECT on a raw block device; the AIO programming model maps quite directly to the NVMe driver programming model (create a queue, submit I/Os, and poll for completions).