On 2/3/22 23:34, Usama Arif wrote:
For opcodes relating to registering/unregistering eventfds, 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 second patch creates the RCU protected data structure and removes ring quiesce for IORING_REGISTER_EVENTFD and IORING_UNREGISTER_EVENTFD. The third patch builds on top of the second patch and removes ring quiesce for IORING_REGISTER_EVENTFD_ASYNC. The fourth patch completely removes ring quiesce from io_uring_register, as IORING_REGISTER_ENABLE_RINGS and IORING_REGISTER_RESTRICTIONS dont need them.
Let me leave it just for history: I strongly dislike it considering there is no one who uses or going to use it. Even more, I can't find a single user of io_uring_unregister_eventfd() in liburing tests, so most probably the paths are not tested at all.
--- v4->v5: - Remove ring quiesce completely from io_uring_register (Pavel Begunkov) - Replaced rcu_barrier with unregistering flag (Jens Axboe) - Created a faster check for ctx->io_ev_fd in io_eventfd_signal and cleaned up io_eventfd_unregister (Jens Axboe) v3->v4: - Switch back to call_rcu and use rcu_barrier incase io_eventfd_register fails to make sure all rcu callbacks have finished. v2->v3: - Switched to using synchronize_rcu from call_rcu in io_eventfd_unregister. v1->v2: - Added patch to remove eventfd from tracepoint (Patch 1) (Jens Axboe) - Made the code of io_should_trigger_evfd as part of io_eventfd_signal (Jens Axboe) Usama Arif (4): io_uring: remove trace for eventfd io_uring: avoid ring quiesce while registering/unregistering eventfd io_uring: avoid ring quiesce for IORING_REGISTER_EVENTFD_ASYNC io_uring: remove ring quiesce for io_uring_register fs/io_uring.c | 202 ++++++++++++++++---------------- include/trace/events/io_uring.h | 13 +- 2 files changed, 107 insertions(+), 108 deletions(-)
-- Pavel Begunkov
