[PATCH 00/17] io_uring passthru over nvme

Kanchan Joshi
2022-03-08T15:42:06Z

This is a streamlined series with new way of doing uring-cmd, and connects
nvme-passthrough (over char device /dev/ngX) to it.
uring-cmd enables using io_uring for any arbitrary command (ioctl,
fsctl etc.) exposed by the command provider (e.g. driver, fs etc.).

To store the command inline within the sqe, Jens added an option to setup
the ring with 128-byte SQEs.This gives 80 bytes of space (16 bytes at
the end of the first sqe + 64 bytes in the second sqe). With inline
command in sqe, the application avoids explicit allocation and, in the
kernel, we avoid doing copy_from_user. Command-opcode, length etc.
are stored in per-op fields of io_uring_sqe.

Non-inline submission (when command is a user-space pointer rather than
housed inside sqe) is also supported.

io_uring sends this command down by newly introduced ->async_cmd()
handler in file_operations. The handler does what is required to
submit, and indicates queued completion.The infra has been added to
process the completion when it arrives.

Overall the patches wire up the following capabilities for this path:
- async
- fixed-buffer
- plugging
- bio-cache
- sync and async polling.

This scales well. 512b randread perf (KIOPS) comparing
uring-passthru-over-char (/dev/ng0n1) to
uring-over-block(/dev/nvme0n1)

QD uring pt uring-poll pt-poll
8 538 589 831 902
64 967 1131 1351 1378
256 1043 1230 1376 1429

Testing/perf is done with this custom fio that turnes regular-io into
passthru-io on supplying "uring_cmd=1" option.
https://github.com/joshkan/fio/tree/big-sqe-pt.v1

Example command-line:
fio -iodepth=256 -rw=randread -ioengine=io_uring -bs=512 -numjobs=1
-runtime=60 -group_reporting -iodepth_batch_submit=64
-iodepth_batch_complete_min=1 -iodepth_batch_complete_max=64
-fixedbufs=1 -hipri=1 -sqthread_poll=0 -filename=/dev/ng0n1
-name=io_uring_256 -uring_cmd=1

Anuj Gupta (3):
io_uring: prep for fixed-buffer enabled uring-cmd
nvme: enable passthrough with fixed-buffer
nvme: enable non-inline passthru commands

Jens Axboe (5):
io_uring: add support for 128-byte SQEs
fs: add file_operations->async_cmd()
io_uring: add infra and support for IORING_OP_URING_CMD
io_uring: plug for async bypass
block: wire-up support for plugging

Kanchan Joshi (5):
nvme: wire-up support for async-passthru on char-device.
io_uring: add support for uring_cmd with fixed-buffer
block: factor out helper for bio allocation from cache
nvme: enable bio-cache for fixed-buffer passthru
io_uring: add support for non-inline uring-cmd

Keith Busch (2):
nvme: modify nvme_alloc_request to take an additional parameter
nvme: allow user passthrough commands to poll

Pankaj Raghav (2):
io_uring: add polling support for uring-cmd
nvme: wire-up polling for uring-passthru

block/bio.c | 43 ++--
block/blk-map.c | 45 +++++
block/blk-mq.c | 93 ++++-----
drivers/nvme/host/core.c | 21 +-
drivers/nvme/host/ioctl.c | 336 +++++++++++++++++++++++++++-----
drivers/nvme/host/multipath.c | 2 +
drivers/nvme/host/nvme.h | 11 +-
drivers/nvme/host/pci.c | 4 +-
drivers/nvme/target/passthru.c | 2 +-
fs/io_uring.c | 188 ++++++++++++++++--
include/linux/bio.h | 1 +
include/linux/blk-mq.h | 4 +
include/linux/fs.h | 2 +
include/linux/io_uring.h | 43 ++++
include/uapi/linux/io_uring.h | 21 +-
include/uapi/linux/nvme_ioctl.h | 4 +
16 files changed, 689 insertions(+), 131 deletions(-)

--
2.25.1