[PATCH v2 0/5] skip request refcounting

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

With some tricks, we can avoid refcounting in most of the cases and
so save on atomics. 1-2 are simple preparations and 3-4 are the meat.
5/5 is a hint to the compiler, which stopped to similarly optimise it
as is.

Jens tried out a prototype before, apparently it gave ~3% win for
the default read test. Not much has changed since then, so I'd
expect same result, and also hope that it should be of even greater
benefit to multithreaded workloads.

The previous version had a flaw, so it was decided to move all
completions out of IRQ and base on that assumption. On top of
io_uring-irq branch.

v2: Rebase to IRQ branch and updated descriptions. Removed prep
    patches. The main part is split in 2: dealing with submission
    refs, and completion. Added 5/5.

Pavel Begunkov (5):
  io_uring: move req_ref_get() and friends
  io_uring: remove req_ref_sub_and_test()
  io_uring: remove submission references
  io_uring: skip request refcounting
  io_uring: optimise hot path of ltimeout prep

 fs/io_uring.c | 173 +++++++++++++++++++++++++++-----------------------
 1 file changed, 94 insertions(+), 79 deletions(-)

-- 
2.32.0