On Thu, Aug 18, 2016 at 8:27 PM, Roman Kagan <rka...@virtuozzo.com> wrote: > Upon save/restore virtio-balloon stats acquisition stops. The reason is > that the fact that the (only) virtqueue element is being used by QEMU is > not recorded anywhere on save, so upon restore it's not released to the > guest, making further progress impossible. > > Saving the information about the used element would introduce unjustified > vmstate incompatibility. > > So instead just make sure the element is pushed before save, leaving the > ball on the guest side. For that, add vm state change handler to > virtio-ballon which would take care of pushing the element if there is > one.
Please take a look at: https://lists.gnu.org/archive/html/qemu-devel/2016-08/msg01038.html virtqueue_discard looks like a better choice than virtqueue_push. There's no need to cause churn on the guest side and receive an extra set of stats in between the regular timer callbacks. Also in that thread see the note about stats_vq_offset which is misused and can be killed. Thanks, Ladi > Signed-off-by: Roman Kagan <rka...@virtuozzo.com> > Cc: "Michael S. Tsirkin" <m...@redhat.com> > --- > hw/virtio/virtio-balloon.c | 27 ++++++++++++++++++++++----- > include/hw/virtio/virtio-balloon.h | 1 + > 2 files changed, 23 insertions(+), 5 deletions(-) > > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c > index b56fecd..66a926a 100644 > --- a/hw/virtio/virtio-balloon.c > +++ b/hw/virtio/virtio-balloon.c > @@ -88,10 +88,19 @@ static void balloon_stats_change_timer(VirtIOBalloon *s, > int64_t secs) > timer_mod(s->stats_timer, qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + secs * > 1000); > } > > +static void balloon_stats_push_elem(VirtIOBalloon *s) > +{ > + VirtIODevice *vdev = VIRTIO_DEVICE(s); > + > + virtqueue_push(s->svq, s->stats_vq_elem, s->stats_vq_offset); > + virtio_notify(vdev, s->svq); > + g_free(s->stats_vq_elem); > + s->stats_vq_elem = NULL; > +} > + > static void balloon_stats_poll_cb(void *opaque) > { > VirtIOBalloon *s = opaque; > - VirtIODevice *vdev = VIRTIO_DEVICE(s); > > if (!s->stats_vq_elem) { > /* The guest hasn't sent the stats yet (either not enabled or we came > @@ -100,10 +109,7 @@ static void balloon_stats_poll_cb(void *opaque) > return; > } > > - virtqueue_push(s->svq, s->stats_vq_elem, s->stats_vq_offset); > - virtio_notify(vdev, s->svq); > - g_free(s->stats_vq_elem); > - s->stats_vq_elem = NULL; > + balloon_stats_push_elem(s); > } > > static void balloon_stats_get_all(Object *obj, Visitor *v, const char *name, > @@ -411,6 +417,15 @@ static int virtio_balloon_load_device(VirtIODevice > *vdev, QEMUFile *f, > return 0; > } > > +static void balloon_vm_state_change(void *opaque, int running, RunState > state) > +{ > + VirtIOBalloon *s = opaque; > + > + if (!running && s->stats_vq_elem) { > + balloon_stats_push_elem(s); > + } > +} > + > static void virtio_balloon_device_realize(DeviceState *dev, Error **errp) > { > VirtIODevice *vdev = VIRTIO_DEVICE(dev); > @@ -433,6 +448,7 @@ static void virtio_balloon_device_realize(DeviceState > *dev, Error **errp) > s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output); > s->svq = virtio_add_queue(vdev, 1, virtio_balloon_receive_stats); > > + s->change = qemu_add_vm_change_state_handler(balloon_vm_state_change, s); > reset_stats(s); > } > > @@ -441,6 +457,7 @@ static void virtio_balloon_device_unrealize(DeviceState > *dev, Error **errp) > VirtIODevice *vdev = VIRTIO_DEVICE(dev); > VirtIOBalloon *s = VIRTIO_BALLOON(dev); > > + qemu_del_vm_change_state_handler(s->change); > balloon_stats_destroy_timer(s); > qemu_remove_balloon_handler(s); > virtio_cleanup(vdev); > diff --git a/include/hw/virtio/virtio-balloon.h > b/include/hw/virtio/virtio-balloon.h > index 1ea13bd..d72ff7f 100644 > --- a/include/hw/virtio/virtio-balloon.h > +++ b/include/hw/virtio/virtio-balloon.h > @@ -43,6 +43,7 @@ typedef struct VirtIOBalloon { > int64_t stats_last_update; > int64_t stats_poll_interval; > uint32_t host_features; > + VMChangeStateEntry *change; > } VirtIOBalloon; > > #endif > -- > 2.7.4 > >