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    SubjectRe: [PATCH v5 0/4] io_uring: remove ring quiesce in io_uring_register
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    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

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