io_uring: add clarifying comment for io_cqring_ev_posted()

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We've previously had an issue where overflow flush unconditionally calls
io_cqring_ev_posted() even if it didn't flush any events to the ring,
causing wake and eventfd increment where no new events are available.
Some applications don't like that, see commit b18032bb0a for details.

This came up in discussion for another patch recently, hence add a
comment detailing what the relationship between calling the events
posted helper and CQ ring entries is.

Link: https://lore.kernel.org/io-uring/77a44fce-c831-16a6-8e80-9aee77f496a2@kernel.dk/
Signed-off-by: Jens Axboe <axboe@kernel.dk>

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Jens Axboe 2021-08-21 07:21:19 -06:00

parent 0bea96f59b

commit 2c5d763c19

1 changed files with 7 additions and 0 deletions

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