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-rw-r--r--drivers/vhost/vhost.c28
-rw-r--r--drivers/vhost/vhost.h3
2 files changed, 25 insertions, 6 deletions
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 2f58181b918d..c0f81e8cb50c 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -290,6 +290,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq->avail = NULL;
vq->used = NULL;
vq->last_avail_idx = 0;
+ vq->last_used_event = 0;
vq->avail_idx = 0;
vq->last_used_idx = 0;
vq->signalled_used = 0;
@@ -1324,7 +1325,7 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
r = -EINVAL;
break;
}
- vq->last_avail_idx = s.num;
+ vq->last_avail_idx = vq->last_used_event = s.num;
/* Forget the cached index value. */
vq->avail_idx = vq->last_avail_idx;
break;
@@ -2159,10 +2160,6 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
__u16 old, new;
__virtio16 event;
bool v;
- /* Flush out used index updates. This is paired
- * with the barrier that the Guest executes when enabling
- * interrupts. */
- smp_mb();
if (vhost_has_feature(vq, VIRTIO_F_NOTIFY_ON_EMPTY) &&
unlikely(vq->avail_idx == vq->last_avail_idx))
@@ -2170,6 +2167,10 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) {
__virtio16 flags;
+ /* Flush out used index updates. This is paired
+ * with the barrier that the Guest executes when enabling
+ * interrupts. */
+ smp_mb();
if (vhost_get_user(vq, flags, &vq->avail->flags)) {
vq_err(vq, "Failed to get flags");
return true;
@@ -2184,11 +2185,26 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
if (unlikely(!v))
return true;
+ /* We're sure if the following conditions are met, there's no
+ * need to notify guest:
+ * 1) cached used event is ahead of new
+ * 2) old to new updating does not cross cached used event. */
+ if (vring_need_event(vq->last_used_event, new + vq->num, new) &&
+ !vring_need_event(vq->last_used_event, new, old))
+ return false;
+
+ /* Flush out used index updates. This is paired
+ * with the barrier that the Guest executes when enabling
+ * interrupts. */
+ smp_mb();
+
if (vhost_get_user(vq, event, vhost_used_event(vq))) {
vq_err(vq, "Failed to get used event idx");
return true;
}
- return vring_need_event(vhost16_to_cpu(vq, event), new, old);
+ vq->last_used_event = vhost16_to_cpu(vq, event);
+
+ return vring_need_event(vq->last_used_event, new, old);
}
/* This actually signals the guest, using eventfd. */
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 78f3c5fc02e4..a9cbbb148f46 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -107,6 +107,9 @@ struct vhost_virtqueue {
/* Last index we used. */
u16 last_used_idx;
+ /* Last used evet we've seen */
+ u16 last_used_event;
+
/* Used flags */
u16 used_flags;