On 6/19/22 12:49 PM, Pavel Begunkov wrote: > On 6/19/22 19:18, Jens Axboe wrote: >> On Sun, Jun 19, 2022 at 5:26 AM Pavel Begunkov <asml.silence@xxxxxxxxx> wrote: >>> >>> Some io_uring-eventfd users assume that there won't be spurious wakeups. >>> That assumption has to be honoured by all io_cqring_ev_posted() callers, >>> which is inconvenient and from time to time leads to problems but should >>> be maintained to not break the userspace. >>> >>> Instead of making the callers to track whether a CQE was posted or not, >>> hide it inside io_eventfd_signal(). It saves ->cached_cq_tail it saw >>> last time and triggers the eventfd only when ->cached_cq_tail changed >>> since then. >> >> This one is causing frequent errors with poll-cancel.t: >> >> axboe@m1pro-kvm ~/g/liburing (master)> test/poll-cancel.t >> axboe@m1pro-kvm ~/g/liburing (master)> test/poll-cancel.t >> Timed out! >> axboe@m1pro-kvm ~/g/liburing (master) [1]> test/poll-cancel.t >> Timed out! >> axboe@m1pro-kvm ~/g/liburing (master) [1]> test/poll-cancel.t >> Timed out! >> >> I've dropped this one, and 6-7/7 as they then also throw a bunch of >> rejects. > > I mentioned it in the cover letter, extra wake ups slowing task > exit cancellations down, which make it to timeout (increasing > alarm time helps). The problem is in cancellation, in particular > because for some reason it spins on the cancellation (including > timeout and poll remove all). But that's not really usable at all. Before the patch, the test case takes 1-2ms, predictably. After the patch, I see lots of 10.0s runs. That's clearly not going to work. -- Jens Axboe
