On 9/3/21 12:00 PM, Hao Xu wrote:
> For operations like accept, multishot is a useful feature, since we can
> reduce a number of accept sqe. Let's integrate it to fast poll, it may
> be good for other operations in the future.
__io_arm_poll_handler() |
-> vfs_poll() |
| io_async_task_func() // post CQE
| ...
| do_apoll_rewait();
-> continues after vfs_poll(),|
removing poll->head of |
the second poll attempt. |
One of the reasons for forbidding multiple apoll's is that it
might be racy. I haven't looked into this implementation, but
we should check if there will be problems from that.
FWIW, putting aside this patchset, the poll/apoll is not in
the best shape and can use some refactoring.
> Signed-off-by: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx>
> ---
> fs/io_uring.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index d6df60c4cdb9..dae7044e0c24 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -5277,8 +5277,15 @@ static void io_async_task_func(struct io_kiocb *req, bool *locked)
> return;
> }
>
> - hash_del(&req->hash_node);
> - io_poll_remove_double(req);
> + if (READ_ONCE(apoll->poll.canceled))
> + apoll->poll.events |= EPOLLONESHOT;
> + if (apoll->poll.events & EPOLLONESHOT) {
> + hash_del(&req->hash_node);
> + io_poll_remove_double(req);
> + } else {
> + add_wait_queue(apoll->poll.head, &apoll->poll.wait);
> + }
> +
> spin_unlock(&ctx->completion_lock);
>
> if (!READ_ONCE(apoll->poll.canceled))
> @@ -5366,7 +5373,7 @@ static int io_arm_poll_handler(struct io_kiocb *req)
> struct io_ring_ctx *ctx = req->ctx;
> struct async_poll *apoll;
> struct io_poll_table ipt;
> - __poll_t ret, mask = EPOLLONESHOT | POLLERR | POLLPRI;
> + __poll_t ret, mask = POLLERR | POLLPRI;
> int rw;
>
> if (!req->file || !file_can_poll(req->file))
> @@ -5388,6 +5395,8 @@ static int io_arm_poll_handler(struct io_kiocb *req)
> rw = WRITE;
> mask |= POLLOUT | POLLWRNORM;
> }
> + if (!(req->flags & REQ_F_APOLL_MULTISHOT))
> + mask |= EPOLLONESHOT;
>
> /* if we can't nonblock try, then no point in arming a poll handler */
> if (!io_file_supports_nowait(req, rw))
>
--
Pavel Begunkov
