[PATCHv3 0/7] dma mapping optimisations

[Keith Busch]

From: Keith Busch <kbusch at kernel.org>

Changes since v2:

  Fixed incorrect io_uring io_fixed_file index validit checksy: this should
  have been validating the file_ptr (Ammar)

  Various micro-optimizations: move up dma in iov type checks, skip
  iov_iter_advance on async IO (Jens).

  NVMe driver cleanups splitting the fast and slow paths.

  NVMe driver prp list setup fixes when using the slow path.

Summary:

A user address undergoes various represenations for a typical read or
write command. 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, 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 '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 reach the hardware's DMA
mapped address format, 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 IOPs.

The implementation is currently limited to mapping a registered buffer
to a single io_uring fixed 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                    |  24 ++-
 block/blk-merge.c              |  19 ++
 block/fops.c                   |  24 ++-
 drivers/nvme/host/pci.c        | 314 +++++++++++++++++++++++++++++++--
 fs/file.c                      |  15 ++
 include/linux/bio.h            |  22 ++-
 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            | 139 +++++++++++++++
 io_uring/net.c                 |   2 +-
 io_uring/rsrc.c                |  27 +--
 io_uring/rsrc.h                |  10 +-
 io_uring/rw.c                  |   2 +-
 lib/iov_iter.c                 |  27 ++-
 22 files changed, 724 insertions(+), 54 deletions(-)

-- 
2.30.2