[PATCH RFC 0/9] nxt propagation + locking optimisation

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

There are several independent parts in the patchset, but bundled
to make a point.
1-2: random stuff, that implicitly used later.
3-5: restore @nxt propagation
6-8: optimise locking in io_worker_handle_work()
9: optimise io_uring refcounting

The next propagation bits are done similarly as it was before, but
- nxt stealing is now at top-level, but not hidden in handlers
- ensure there is no with REQ_F_DONT_STEAL_NEXT

[6-8] is the reason to dismiss the previous @nxt propagation appoach,
I didn't found a good way to do the same. Even though it looked
clearer and without new flag.

Performance tested it with link-of-nops + IOSQE_ASYNC:

link size: 100
orig:  501 (ns per nop)
0-8:   446
0-9:   416

link size: 10
orig:  826
0-8:   776
0-9:   756

Pavel Begunkov (9):
  io_uring: clean up io_close
  io-wq: fix IO_WQ_WORK_NO_CANCEL cancellation
  io_uring: make submission ref putting consistent
  io_uring: remove @nxt from handlers
  io_uring: get next req on subm ref drop
  io-wq: shuffle io_worker_handle_work() code
  io-wq: io_worker_handle_work() optimise locking
  io-wq: optimise double lock for io_get_next_work()
  io_uring: pass submission ref to async

 fs/io-wq.c    | 162 ++++++++++++----------
 fs/io_uring.c | 366 ++++++++++++++++++++++----------------------------
 2 files changed, 258 insertions(+), 270 deletions(-)

-- 
2.24.0