[RFC v2 0/5] BPF controlled io_uring

[Pavel Begunkov <asml.silence@gmail.com>]

This series adds io_uring BPF struct_ops, which allows processing
events and submitting requests from BPF without returning to user.
There is only one callback for now, it's called from the io_uring
CQ waiting loop when there is an event to be processed. It also
has access to waiting parameters like batching and timeouts.

It's tested with a program that queues a nop request, waits for
its completion and then queues another request, repeating it N
times. The baseline to compare with is traditional io_uring
application doing same without BPF and using 2 requests links,
with the same total number of requests.

# ./link 0 100000000
type 2-LINK, requests to run 100000000
sec 20, total (ms) 20374
# ./link 1 100000000
type BPF, requests to run 100000000
sec 13, total (ms) 13700

The BPF version works ~50% faster on a mitigated kernel, while it's
not even a completely fair comparison as links are restrictive and
can't always be used. Without links the speedup reaches ~80%.

This allows arbitrary relations between requests including using
a result from one request to configure the following one. There are
other use cases in mind that need access to in-kernel resources and
can't be implemented from userspace. On top, it can be extended with
more callbacks to get finer control over task work batching.

It's a prototype, I intend to remake the kfunc helpers, enchance
program verification, and fix some mild io_uring waiting edge
cases.

Kernel branch:
https://github.com/isilence/linux/tree/io-uring-bpf/v2
git https://github.com/isilence/linux.git io-uring-bpf/v2

Liburing + bpf bootsrap examples:
https://github.com/isilence/liburing/tree/bpf-struct-ops-examples
git git@github.com:isilence/liburing.git bpf-struct-ops-examples

Pavel Begunkov (5):
  io_uring: add struct for state controlling cqwait
  io_uring/bpf: add stubs for bpf struct_ops
  io_uring/bpf: implement struct_ops registration
  io_uring/bpf: add handle events callback
  io_uring/bpf: add basic kfunc helpers

 include/linux/io_uring_types.h |   4 +
 io_uring/Kconfig               |   5 +
 io_uring/Makefile              |   1 +
 io_uring/bpf.c                 | 277 +++++++++++++++++++++++++++++++++
 io_uring/bpf.h                 |  45 ++++++
 io_uring/io_uring.c            |  45 ++++--
 io_uring/io_uring.h            |  11 +-
 io_uring/napi.c                |   4 +-
 8 files changed, 376 insertions(+), 16 deletions(-)
 create mode 100644 io_uring/bpf.c
 create mode 100644 io_uring/bpf.h

-- 
2.49.0