Am 03.08.20 um 18:41 schrieb Jens Axboe: > On 8/2/20 9:16 PM, Jiufei Xue wrote: >> Hi Jens, >> >> On 2020/7/31 上午11:57, Jens Axboe wrote: >>> Then why not just make the sqe-less timeout path flush existing requests, >>> if it needs to? Seems a lot simpler than adding odd x2 variants, which >>> won't really be clear. >>> >> Flushing the requests will access and modify the head of submit queue, that >> may race with the submit thread. I think the reap thread should not touch >> the submit queue when IORING_FEAT_GETEVENTS_TIMEOUT is supported. > > Ahhh, that's the clue I was missing, yes that's a good point! > >>> Chances are, if it's called with sq entries pending, the caller likely >>> wants those submitted. Either the caller was aware and relying on that >>> behavior, or the caller is simply buggy and has a case where it doesn't >>> submit IO before waiting for completions. >>> >> >> That is not true when the SQ/CQ handling are split in two different threads. >> The reaping thread is not aware of the submit queue. It should only wait for >> completion of the requests, such as below: >> >> submitting_thread: reaping_thread: >> >> io_uring_get_sqe() >> io_uring_prep_nop() >> io_uring_wait_cqe_timeout2() >> io_uring_submit() >> woken if requests are completed or timeout >> >> >> And if the SQ/CQ handling are in the same thread, applications should use the >> old API if they do not want to submit the request themselves. >> >> io_uring_get_sqe >> io_uring_prep_nop >> io_uring_wait_cqe_timeout > > Thanks, yes it's all clear to me now. I do wonder if we can't come up with > something better than postfixing the functions with a 2, that seems kind of > ugly and doesn't really convey to anyone what the difference is. > > Any suggestions for better naming? Isn't a bit in ring->flags enough? Instead of a new function? Also the struct passed to the kernel should be a named one instead of an anonymous struct defined in two places. Maybe a wrapping union would be good... metze
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