Re: [RFC 0/3] aio-posix: call ->poll_end() when removing AioHandler

[Paolo Bonzini]

On Tue, Jan 2, 2024 at 4:24 PM Hanna Czenczek <hreitz@redhat.com> wrote:
> I’ve attached the preliminary patch that I didn’t get to send (or test
> much) last year.  Not sure if it has the same CPU-usage-spike issue
> Fiona was seeing, the only functional difference is that I notify the vq
> after attaching the notifiers instead of before.

I think the patch makes sense and cleaning up the logic of aio_poll
(which is one of those functions that grew and grew without much
clarity into who did what) can be done on top.

Just one small thing, the virtio_queue_notify_vq() call is required
because the virtqueue interrupt and eventfd are edge-triggered rather
than level-triggered; so perhaps it should be placed in the
function(s) that establish the handlers,
virtio_queue_aio_attach_host_notifier() and
virtio_queue_aio_attach_host_notifier_no_poll()? Neither
virtio_blk_drained_end() nor virtio_scsi_drained_end() are
particularly special, and the comment applies just as well:

    /*
     * We will have ignored notifications about new requests from the guest
     * while handlers were not attached, so "kick" the virt queue to process
     * those requests now.
     */

Paolo