Curently we will keep polling when there is no free slot.

if let Some(slot) = future.uring.submit(sqe) {
    // ...
} else {
    // There is no free slot.
    // We expect that wake_by_ref() will put the task at tail of task queue.
    // But Tokio will put the task at "next task" slot, so it will run again immediately.
    cx.waker().wake_by_ref();
    return Poll::Pending;
}

I am working to remove the polling. I will save the waker in the free list when there is no slot, and invoke waker.wake() when others release the slot.

After thinking about it, it's not a good practice to use kbio alone. In this case, Walker.Wake() occurs in kbio's own thread, and it needs a cross thread communication to submit task to Tokio runtime.

It is better to directly replace Tokio IO::driver from Mio to io-uring, in this way, IO tasks are directly submitted to the current thread. Iouring and wake() will also occur on the same thread. At this time, cross thread thread communication will generally only occur in the case of work steal.