Messages in this thread | | | Date | Fri, 4 Feb 2022 00:02:08 +0000 | Subject | Re: [PATCH v5 0/4] io_uring: remove ring quiesce in io_uring_register | From | Pavel Begunkov <> |
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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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