On 2/6/20 10:33 AM, Stefano Garzarella wrote: > > > On Fri, Jan 31, 2020 at 4:39 PM Jens Axboe <axboe@xxxxxxxxx> wrote: >> >> On 1/31/20 7:29 AM, Stefano Garzarella wrote: >>> Hi Jens, >>> this is a v2 of the epoll test. >>> >>> v1 -> v2: >>> - if IORING_FEAT_NODROP is not available, avoid to overflow the CQ >>> - add 2 new tests to test epoll with IORING_FEAT_NODROP >>> - cleanups >>> >>> There are 4 sub-tests: >>> 1. test_epoll >>> 2. test_epoll_sqpoll >>> 3. test_epoll_nodrop >>> 4. test_epoll_sqpoll_nodrop >>> >>> In the first 2 tests, I try to avoid to queue more requests than we have room >>> for in the CQ ring. These work fine, I have no faults. >> >> Thanks! >> >>> In the tests 3 and 4, if IORING_FEAT_NODROP is supported, I try to submit as >>> much as I can until I get a -EBUSY, but they often fail in this way: >>> the submitter manages to submit everything, the receiver receives all the >>> submitted bytes, but the cleaner loses completion events (I also tried to put a >>> timeout to epoll_wait() in the cleaner to be sure that it is not related to the >>> patch that I send some weeks ago, but the situation doesn't change, it's like >>> there is still overflow in the CQ). >>> >>> Next week I'll try to investigate better which is the problem. >> >> Does it change if you have an io_uring_enter() with GETEVENTS set? I wonder if >> you just pruned the CQ ring but didn't flush the internal side. > > If I do io_uring_enter() with GETEVENTS set and wait_nr = 0 it solves > the issue, I think because we call io_cqring_events() that flushes the > overflow list. > > At this point, should we call io_cqring_events() (that flushes the > overflow list) in io_uring_poll()? > I mean something like this: > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index 77f22c3da30f..2769451af89a 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -6301,7 +6301,7 @@ static __poll_t io_uring_poll(struct file *file, poll_table *wait) > if (READ_ONCE(ctx->rings->sq.tail) - ctx->cached_sq_head != > ctx->rings->sq_ring_entries) > mask |= EPOLLOUT | EPOLLWRNORM; > - if (READ_ONCE(ctx->rings->cq.head) != ctx->cached_cq_tail) > + if (!io_cqring_events(ctx, false)) > mask |= EPOLLIN | EPOLLRDNORM; > > return mask; That's not a bad idea, would just have to verify that it is indeed safe to always call the flushing variant from there. -- Jens Axboe
