[PATCH 0/2] io_uring: avoid ring quiesce in io_uring_register for eventfd opcodes

[Usama Arif <usama.arif@bytedance.com>]

This is done by creating a new RCU data structure (io_ev_fd) as part of
io_ring_ctx that holds the eventfd_ctx, with reads to the structure protected
by rcu_read_lock and writes (register/unregister calls) protected by a mutex.

With the above approach ring quiesce can be avoided which is much more
expensive then using RCU lock. On the system tested, io_uring_reigster with
IORING_REGISTER_EVENTFD takes less than 1ms with RCU lock, compared to 15ms
before with ring quiesce.

The first patch creates the RCU protected data structure and removes ring
quiesce for IORING_REGISTER_EVENTFD and IORING_UNREGISTER_EVENTFD.

The second patch builds on top of the first patch and removes ring quiesce
for IORING_REGISTER_EVENTFD_ASYNC.

Usama Arif (2):
  io_uring: avoid ring quiesce while registering/unregistering eventfd
  io_uring: avoid ring quiesce for IORING_REGISTER_EVENTFD_ASYNC

 fs/io_uring.c | 125 +++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 92 insertions(+), 33 deletions(-)

-- 
2.25.1