[Qemu-devel] [PATCH 3/4] virtio-balloon: don't restart stats timer in callback

[Roman Kagan <rkagan@virtuozzo.com>]

There's no need to restart the stats timer in its callback.  If the
callback happens to run when there's nothing to do just do nothing and
return.

The timer is armed either in receive handler or initially when
periodic stats collection is enabled via QMP.

While at this, observe that the presence of ->stats_vq_elem is enough to
indicate there's work to do here, and drop the check for the stats
feature.

Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
---
 hw/virtio/virtio-balloon.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index 0baf4b3..b56fecd 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -68,12 +68,6 @@ static inline void reset_stats(VirtIOBalloon *dev)
     for (i = 0; i < VIRTIO_BALLOON_S_NR; dev->stats[i++] = -1);
 }
 
-static bool balloon_stats_supported(const VirtIOBalloon *s)
-{
-    VirtIODevice *vdev = VIRTIO_DEVICE(s);
-    return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_STATS_VQ);
-}
-
 static bool balloon_stats_enabled(const VirtIOBalloon *s)
 {
     return s->stats_poll_interval > 0;
@@ -99,9 +93,10 @@ static void balloon_stats_poll_cb(void *opaque)
     VirtIOBalloon *s = opaque;
     VirtIODevice *vdev = VIRTIO_DEVICE(s);
 
-    if (s->stats_vq_elem == NULL || !balloon_stats_supported(s)) {
-        /* re-schedule */
-        balloon_stats_change_timer(s, s->stats_poll_interval);
+    if (!s->stats_vq_elem) {
+        /* The guest hasn't sent the stats yet (either not enabled or we came
+         * too early), nothing to do.  Once the guest starts sending stats the
+         * timer will get armed in receive handler */
         return;
     }
 
-- 
2.7.4