From: Keith Busch <kbusch@xxxxxxxxxx> Changes since v1: Mapping/unmapping goes through file ops instead of block device ops. This abstracts io_uring from knowing about specific block devices. For this series, the only "file system" implementing the ops is the raw block device, but should be easy enough to add more filesystems if needed. Mapping register requires io_uring fixed files. This ties the registered buffer's lifetime to no more than the file it was registered with. Summary: A typical journey a user address takes for a read or write to a block device undergoes various represenations for every IO. Each consumes memory and CPU cycles. When the backing storage is NVMe, the sequence looks something like the following: __user void * struct iov_iter struct pages[] struct bio_vec[] struct scatterlist[] __le64[] Applications will often use the same buffer for many IO, though, so these potentially costly per-IO transformations to reach the exact same hardware descriptor can be skipped. The io_uring interface already provides a way for users to register buffers to get to the 'struct bio_vec[]'. That still leaves the scatterlist needed for the repeated dma_map_sg(), then transform to nvme's PRP list format. This series takes the registered buffers a step further. A block driver can implement a new .dma_map() callback to complete the representation to the hardware's DMA mapped address, and return a cookie so a user can reference it later for any given IO. When used, the block stack can skip significant amounts of code, improving CPU utilization, and, if not bandwidth limited, IOPs. The implementation is currently limited to mapping a registered buffer to a single file. Keith Busch (7): blk-mq: add ops to dma map bvec file: add ops to dma map bvec iov_iter: introduce type for preregistered dma tags block: add dma tag bio type io_uring: introduce file slot release helper io_uring: add support for dma pre-mapping nvme-pci: implement dma_map support block/bdev.c | 20 +++ block/bio.c | 25 ++- block/blk-merge.c | 19 +++ block/fops.c | 20 +++ drivers/nvme/host/pci.c | 302 +++++++++++++++++++++++++++++++-- fs/file.c | 15 ++ include/linux/bio.h | 21 ++- include/linux/blk-mq.h | 24 +++ include/linux/blk_types.h | 6 +- include/linux/blkdev.h | 16 ++ include/linux/fs.h | 20 +++ include/linux/io_uring_types.h | 2 + include/linux/uio.h | 9 + include/uapi/linux/io_uring.h | 12 ++ io_uring/filetable.c | 34 ++-- io_uring/filetable.h | 10 +- io_uring/io_uring.c | 137 +++++++++++++++ io_uring/net.c | 2 +- io_uring/rsrc.c | 26 +-- io_uring/rsrc.h | 10 +- io_uring/rw.c | 2 +- lib/iov_iter.c | 24 ++- 22 files changed, 704 insertions(+), 52 deletions(-) -- 2.30.2
