diff mbox series

[[RFC,v3,08/12] virtio: event suppression support for packed ring

Message ID 1539266915-15216-9-git-send-email-wexu@redhat.com (mailing list archive)
State New, archived
Headers show
Series packed ring virtio-net userspace backend support | expand

Commit Message

Wei Xu Oct. 11, 2018, 2:08 p.m. UTC 
From: Wei Xu <wexu@redhat.com>

Signed-off-by: Wei Xu <wexu@redhat.com>
---
 hw/virtio/virtio.c | 126 +++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 123 insertions(+), 3 deletions(-)

Comments

Jason Wang Oct. 15, 2018, 6:55 a.m. UTC | #1 
On 2018年10月11日 22:08, wexu@redhat.com wrote:
> From: Wei Xu <wexu@redhat.com>
>
> Signed-off-by: Wei Xu <wexu@redhat.com>
> ---
>   hw/virtio/virtio.c | 126 +++++++++++++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 123 insertions(+), 3 deletions(-)
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index d12a7e3..1d25776 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -241,6 +241,30 @@ static void vring_desc_read(VirtIODevice *vdev, VRingDesc *desc,
>       virtio_tswap16s(vdev, &desc->next);
>   }
>   
> +static void vring_packed_event_read(VirtIODevice *vdev,
> +                            MemoryRegionCache *cache, VRingPackedDescEvent *e)
> +{
> +    address_space_read_cached(cache, 0, e, sizeof(*e));
> +    virtio_tswap16s(vdev, &e->off_wrap);
> +    virtio_tswap16s(vdev, &e->flags);
> +}
> +
> +static void vring_packed_off_wrap_write(VirtIODevice *vdev,
> +                            MemoryRegionCache *cache, uint16_t off_wrap)
> +{
> +    virtio_tswap16s(vdev, &off_wrap);
> +    address_space_write_cached(cache, 0, &off_wrap, sizeof(off_wrap));
> +    address_space_cache_invalidate(cache, 0, sizeof(off_wrap));
> +}
> +
> +static void vring_packed_flags_write(VirtIODevice *vdev,
> +                            MemoryRegionCache *cache, uint16_t flags)
> +{
> +    virtio_tswap16s(vdev, &flags);
> +    address_space_write_cached(cache, sizeof(uint16_t), &flags, sizeof(flags));
> +    address_space_cache_invalidate(cache, sizeof(uint16_t), sizeof(flags));
> +}
> +
>   static VRingMemoryRegionCaches *vring_get_region_caches(struct VirtQueue *vq)
>   {
>       VRingMemoryRegionCaches *caches = atomic_rcu_read(&vq->vring.caches);
> @@ -347,7 +371,7 @@ static inline void vring_set_avail_event(VirtQueue *vq, uint16_t val)
>       address_space_cache_invalidate(&caches->used, pa, sizeof(val));
>   }
>   
> -void virtio_queue_set_notification(VirtQueue *vq, int enable)
> +static void virtio_queue_set_notification_split(VirtQueue *vq, int enable)
>   {
>       vq->notification = enable;
>   
> @@ -370,6 +394,51 @@ void virtio_queue_set_notification(VirtQueue *vq, int enable)
>       rcu_read_unlock();
>   }
>   
> +static void virtio_queue_set_notification_packed(VirtQueue *vq, int enable)
> +{
> +    VRingPackedDescEvent e;
> +    VRingMemoryRegionCaches *caches;
> +
> +    rcu_read_lock();
> +    caches  = vring_get_region_caches(vq);
> +    vring_packed_event_read(vq->vdev, &caches->device, &e);
> +
> +    if (!enable) {
> +        e.flags = RING_EVENT_FLAGS_DISABLE;
> +        goto out;
> +    }
> +
> +    e.flags = RING_EVENT_FLAGS_ENABLE;
> +    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
> +        uint16_t off_wrap = vq->event_idx | vq->event_wrap_counter << 15;
> +
> +        vring_packed_off_wrap_write(vq->vdev, &caches->device, off_wrap);
> +        /* Make sure off_wrap is wrote before flags */
> +        smp_wmb();
> +
> +        e.flags = RING_EVENT_FLAGS_DESC;
> +    }
> +
> +out:
> +    vring_packed_flags_write(vq->vdev, &caches->device, e.flags);
> +    rcu_read_unlock();
> +}
> +
> +void virtio_queue_set_notification(VirtQueue *vq, int enable)
> +{
> +    vq->notification = enable;
> +
> +    if (!vq->vring.desc) {
> +        return;
> +    }
> +
> +    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
> +        virtio_queue_set_notification_packed(vq, enable);
> +    } else {
> +        virtio_queue_set_notification_split(vq, enable);
> +    }
> +}
> +
>   int virtio_queue_ready(VirtQueue *vq)
>   {
>       return vq->vring.avail != 0;
> @@ -2103,8 +2172,7 @@ static void virtio_set_isr(VirtIODevice *vdev, int value)
>       }
>   }
>   
> -/* Called within rcu_read_lock().  */
> -static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> +static bool virtio_split_should_notify(VirtIODevice *vdev, VirtQueue *vq)
>   {
>       uint16_t old, new;
>       bool v;
> @@ -2127,6 +2195,58 @@ static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
>       return !v || vring_need_event(vring_get_used_event(vq), new, old);
>   }
>   
> +static bool vring_packed_need_event(VirtQueue *vq, uint16_t off_wrap,
> +                                    uint16_t new, uint16_t old)
> +{
> +    bool wrap = vq->event_wrap_counter;
> +    int off = off_wrap & ~(1 << 15);
> +
> +    if (new < old) {
> +        new += vq->vring.num;
> +        wrap ^= 1;
> +    }
> +
> +    if (wrap != off_wrap >> 15) {
> +        off += vq->vring.num;
> +    }

Let's use a more compact and verified version from dpdk:

static bool vhost_vring_packed_need_event(struct vhost_virtqueue *vq,
                       bool wrap, __u16 off_wrap, __u16 new,
                       __u16 old)
{
     int off = off_wrap & ~(1 << 15);

     if (wrap != off_wrap >> 15)
         off -= vq->num;

     return vring_need_event(off, new, old);
}

Thanks

> +
> +    return vring_need_event(off, new, old);
> +}
> +
> +static bool virtio_packed_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> +{
> +    VRingPackedDescEvent e;
> +    uint16_t old, new;
> +    bool v;
> +    VRingMemoryRegionCaches *caches;
> +
> +    caches  = vring_get_region_caches(vq);
> +    vring_packed_event_read(vdev, &caches->driver, &e);
> +
> +    old = vq->signalled_used;
> +    new = vq->signalled_used = vq->used_idx;
> +    v = vq->signalled_used_valid;
> +    vq->signalled_used_valid = true;
> +
> +    if (e.flags == RING_EVENT_FLAGS_DISABLE) {
> +        return false;
> +    } else if (e.flags == RING_EVENT_FLAGS_ENABLE) {
> +        return true;
> +    }
> +
> +    return !v || vring_packed_need_event(vq, e.off_wrap, new, old);
> +}
> +
> +/* Called within rcu_read_lock().  */
> +static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> +{
> +    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> +        return virtio_packed_should_notify(vdev, vq);
> +    } else {
> +        return virtio_split_should_notify(vdev, vq);
> +    }
> +}
> +
>   void virtio_notify_irqfd(VirtIODevice *vdev, VirtQueue *vq)
>   {
>       bool should_notify;
Jason Wang Oct. 15, 2018, 6:59 a.m. UTC | #2 
On 2018年10月11日 22:08, wexu@redhat.com wrote:
> From: Wei Xu <wexu@redhat.com>
>
> Signed-off-by: Wei Xu <wexu@redhat.com>
> ---
>   hw/virtio/virtio.c | 126 +++++++++++++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 123 insertions(+), 3 deletions(-)
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index d12a7e3..1d25776 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -241,6 +241,30 @@ static void vring_desc_read(VirtIODevice *vdev, VRingDesc *desc,
>       virtio_tswap16s(vdev, &desc->next);
>   }
>   
> +static void vring_packed_event_read(VirtIODevice *vdev,
> +                            MemoryRegionCache *cache, VRingPackedDescEvent *e)
> +{
> +    address_space_read_cached(cache, 0, e, sizeof(*e));
> +    virtio_tswap16s(vdev, &e->off_wrap);
> +    virtio_tswap16s(vdev, &e->flags);
> +}
> +
> +static void vring_packed_off_wrap_write(VirtIODevice *vdev,
> +                            MemoryRegionCache *cache, uint16_t off_wrap)
> +{
> +    virtio_tswap16s(vdev, &off_wrap);
> +    address_space_write_cached(cache, 0, &off_wrap, sizeof(off_wrap));
> +    address_space_cache_invalidate(cache, 0, sizeof(off_wrap));
> +}
> +
> +static void vring_packed_flags_write(VirtIODevice *vdev,
> +                            MemoryRegionCache *cache, uint16_t flags)
> +{
> +    virtio_tswap16s(vdev, &flags);
> +    address_space_write_cached(cache, sizeof(uint16_t), &flags, sizeof(flags));
> +    address_space_cache_invalidate(cache, sizeof(uint16_t), sizeof(flags));
> +}
> +
>   static VRingMemoryRegionCaches *vring_get_region_caches(struct VirtQueue *vq)
>   {
>       VRingMemoryRegionCaches *caches = atomic_rcu_read(&vq->vring.caches);
> @@ -347,7 +371,7 @@ static inline void vring_set_avail_event(VirtQueue *vq, uint16_t val)
>       address_space_cache_invalidate(&caches->used, pa, sizeof(val));
>   }
>   
> -void virtio_queue_set_notification(VirtQueue *vq, int enable)
> +static void virtio_queue_set_notification_split(VirtQueue *vq, int enable)
>   {
>       vq->notification = enable;
>   
> @@ -370,6 +394,51 @@ void virtio_queue_set_notification(VirtQueue *vq, int enable)
>       rcu_read_unlock();
>   }
>   
> +static void virtio_queue_set_notification_packed(VirtQueue *vq, int enable)
> +{
> +    VRingPackedDescEvent e;
> +    VRingMemoryRegionCaches *caches;
> +
> +    rcu_read_lock();
> +    caches  = vring_get_region_caches(vq);
> +    vring_packed_event_read(vq->vdev, &caches->device, &e);
> +
> +    if (!enable) {
> +        e.flags = RING_EVENT_FLAGS_DISABLE;
> +        goto out;
> +    }
> +
> +    e.flags = RING_EVENT_FLAGS_ENABLE;
> +    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
> +        uint16_t off_wrap = vq->event_idx | vq->event_wrap_counter << 15;

Btw, why not just use shadow_avail_idx here?

Thanks

> +
> +        vring_packed_off_wrap_write(vq->vdev, &caches->device, off_wrap);
> +        /* Make sure off_wrap is wrote before flags */
> +        smp_wmb();
> +
> +        e.flags = RING_EVENT_FLAGS_DESC;
> +    }
> +
> +out:
> +    vring_packed_flags_write(vq->vdev, &caches->device, e.flags);
> +    rcu_read_unlock();
> +}
> +
> +void virtio_queue_set_notification(VirtQueue *vq, int enable)
> +{
> +    vq->notification = enable;
> +
> +    if (!vq->vring.desc) {
> +        return;
> +    }
> +
> +    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
> +        virtio_queue_set_notification_packed(vq, enable);
> +    } else {
> +        virtio_queue_set_notification_split(vq, enable);
> +    }
> +}
> +
>   int virtio_queue_ready(VirtQueue *vq)
>   {
>       return vq->vring.avail != 0;
> @@ -2103,8 +2172,7 @@ static void virtio_set_isr(VirtIODevice *vdev, int value)
>       }
>   }
>   
> -/* Called within rcu_read_lock().  */
> -static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> +static bool virtio_split_should_notify(VirtIODevice *vdev, VirtQueue *vq)
>   {
>       uint16_t old, new;
>       bool v;
> @@ -2127,6 +2195,58 @@ static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
>       return !v || vring_need_event(vring_get_used_event(vq), new, old);
>   }
>   
> +static bool vring_packed_need_event(VirtQueue *vq, uint16_t off_wrap,
> +                                    uint16_t new, uint16_t old)
> +{
> +    bool wrap = vq->event_wrap_counter;
> +    int off = off_wrap & ~(1 << 15);
> +
> +    if (new < old) {
> +        new += vq->vring.num;
> +        wrap ^= 1;
> +    }
> +
> +    if (wrap != off_wrap >> 15) {
> +        off += vq->vring.num;
> +    }
> +
> +    return vring_need_event(off, new, old);
> +}
> +
> +static bool virtio_packed_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> +{
> +    VRingPackedDescEvent e;
> +    uint16_t old, new;
> +    bool v;
> +    VRingMemoryRegionCaches *caches;
> +
> +    caches  = vring_get_region_caches(vq);
> +    vring_packed_event_read(vdev, &caches->driver, &e);
> +
> +    old = vq->signalled_used;
> +    new = vq->signalled_used = vq->used_idx;
> +    v = vq->signalled_used_valid;
> +    vq->signalled_used_valid = true;
> +
> +    if (e.flags == RING_EVENT_FLAGS_DISABLE) {
> +        return false;
> +    } else if (e.flags == RING_EVENT_FLAGS_ENABLE) {
> +        return true;
> +    }
> +
> +    return !v || vring_packed_need_event(vq, e.off_wrap, new, old);
> +}
> +
> +/* Called within rcu_read_lock().  */
> +static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> +{
> +    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> +        return virtio_packed_should_notify(vdev, vq);
> +    } else {
> +        return virtio_split_should_notify(vdev, vq);
> +    }
> +}
> +
>   void virtio_notify_irqfd(VirtIODevice *vdev, VirtQueue *vq)
>   {
>       bool should_notify;
Wei Xu Oct. 15, 2018, 8:20 a.m. UTC | #3 
On Mon, Oct 15, 2018 at 02:59:48PM +0800, Jason Wang wrote:
> 
> 
> On 2018年10月11日 22:08, wexu@redhat.com wrote:
> >From: Wei Xu <wexu@redhat.com>
> >
> >Signed-off-by: Wei Xu <wexu@redhat.com>
> >---
> >  hw/virtio/virtio.c | 126 +++++++++++++++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 123 insertions(+), 3 deletions(-)
> >
> >diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> >index d12a7e3..1d25776 100644
> >--- a/hw/virtio/virtio.c
> >+++ b/hw/virtio/virtio.c
> >@@ -241,6 +241,30 @@ static void vring_desc_read(VirtIODevice *vdev, VRingDesc *desc,
> >      virtio_tswap16s(vdev, &desc->next);
> >  }
> >+static void vring_packed_event_read(VirtIODevice *vdev,
> >+                            MemoryRegionCache *cache, VRingPackedDescEvent *e)
> >+{
> >+    address_space_read_cached(cache, 0, e, sizeof(*e));
> >+    virtio_tswap16s(vdev, &e->off_wrap);
> >+    virtio_tswap16s(vdev, &e->flags);
> >+}
> >+
> >+static void vring_packed_off_wrap_write(VirtIODevice *vdev,
> >+                            MemoryRegionCache *cache, uint16_t off_wrap)
> >+{
> >+    virtio_tswap16s(vdev, &off_wrap);
> >+    address_space_write_cached(cache, 0, &off_wrap, sizeof(off_wrap));
> >+    address_space_cache_invalidate(cache, 0, sizeof(off_wrap));
> >+}
> >+
> >+static void vring_packed_flags_write(VirtIODevice *vdev,
> >+                            MemoryRegionCache *cache, uint16_t flags)
> >+{
> >+    virtio_tswap16s(vdev, &flags);
> >+    address_space_write_cached(cache, sizeof(uint16_t), &flags, sizeof(flags));
> >+    address_space_cache_invalidate(cache, sizeof(uint16_t), sizeof(flags));
> >+}
> >+
> >  static VRingMemoryRegionCaches *vring_get_region_caches(struct VirtQueue *vq)
> >  {
> >      VRingMemoryRegionCaches *caches = atomic_rcu_read(&vq->vring.caches);
> >@@ -347,7 +371,7 @@ static inline void vring_set_avail_event(VirtQueue *vq, uint16_t val)
> >      address_space_cache_invalidate(&caches->used, pa, sizeof(val));
> >  }
> >-void virtio_queue_set_notification(VirtQueue *vq, int enable)
> >+static void virtio_queue_set_notification_split(VirtQueue *vq, int enable)
> >  {
> >      vq->notification = enable;
> >@@ -370,6 +394,51 @@ void virtio_queue_set_notification(VirtQueue *vq, int enable)
> >      rcu_read_unlock();
> >  }
> >+static void virtio_queue_set_notification_packed(VirtQueue *vq, int enable)
> >+{
> >+    VRingPackedDescEvent e;
> >+    VRingMemoryRegionCaches *caches;
> >+
> >+    rcu_read_lock();
> >+    caches  = vring_get_region_caches(vq);
> >+    vring_packed_event_read(vq->vdev, &caches->device, &e);
> >+
> >+    if (!enable) {
> >+        e.flags = RING_EVENT_FLAGS_DISABLE;
> >+        goto out;
> >+    }
> >+
> >+    e.flags = RING_EVENT_FLAGS_ENABLE;
> >+    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
> >+        uint16_t off_wrap = vq->event_idx | vq->event_wrap_counter << 15;
> 
> Btw, why not just use shadow_avail_idx here?

It is nice to do that but an issue here is that it is 'shadow_avail_idx' for
Rx but 'used_idx' for Tx when setting up for a kick, haven't figured out a
clear fix because it helps easier migration part work, any idea?

Wei

> 
> Thanks
> 
> >+
> >+        vring_packed_off_wrap_write(vq->vdev, &caches->device, off_wrap);
> >+        /* Make sure off_wrap is wrote before flags */
> >+        smp_wmb();
> >+
> >+        e.flags = RING_EVENT_FLAGS_DESC;
> >+    }
> >+
> >+out:
> >+    vring_packed_flags_write(vq->vdev, &caches->device, e.flags);
> >+    rcu_read_unlock();
> >+}
> >+
> >+void virtio_queue_set_notification(VirtQueue *vq, int enable)
> >+{
> >+    vq->notification = enable;
> >+
> >+    if (!vq->vring.desc) {
> >+        return;
> >+    }
> >+
> >+    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
> >+        virtio_queue_set_notification_packed(vq, enable);
> >+    } else {
> >+        virtio_queue_set_notification_split(vq, enable);
> >+    }
> >+}
> >+
> >  int virtio_queue_ready(VirtQueue *vq)
> >  {
> >      return vq->vring.avail != 0;
> >@@ -2103,8 +2172,7 @@ static void virtio_set_isr(VirtIODevice *vdev, int value)
> >      }
> >  }
> >-/* Called within rcu_read_lock().  */
> >-static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> >+static bool virtio_split_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> >  {
> >      uint16_t old, new;
> >      bool v;
> >@@ -2127,6 +2195,58 @@ static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> >      return !v || vring_need_event(vring_get_used_event(vq), new, old);
> >  }
> >+static bool vring_packed_need_event(VirtQueue *vq, uint16_t off_wrap,
> >+                                    uint16_t new, uint16_t old)
> >+{
> >+    bool wrap = vq->event_wrap_counter;
> >+    int off = off_wrap & ~(1 << 15);
> >+
> >+    if (new < old) {
> >+        new += vq->vring.num;
> >+        wrap ^= 1;
> >+    }
> >+
> >+    if (wrap != off_wrap >> 15) {
> >+        off += vq->vring.num;
> >+    }
> >+
> >+    return vring_need_event(off, new, old);
> >+}
> >+
> >+static bool virtio_packed_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> >+{
> >+    VRingPackedDescEvent e;
> >+    uint16_t old, new;
> >+    bool v;
> >+    VRingMemoryRegionCaches *caches;
> >+
> >+    caches  = vring_get_region_caches(vq);
> >+    vring_packed_event_read(vdev, &caches->driver, &e);
> >+
> >+    old = vq->signalled_used;
> >+    new = vq->signalled_used = vq->used_idx;
> >+    v = vq->signalled_used_valid;
> >+    vq->signalled_used_valid = true;
> >+
> >+    if (e.flags == RING_EVENT_FLAGS_DISABLE) {
> >+        return false;
> >+    } else if (e.flags == RING_EVENT_FLAGS_ENABLE) {
> >+        return true;
> >+    }
> >+
> >+    return !v || vring_packed_need_event(vq, e.off_wrap, new, old);
> >+}
> >+
> >+/* Called within rcu_read_lock().  */
> >+static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
> >+{
> >+    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> >+        return virtio_packed_should_notify(vdev, vq);
> >+    } else {
> >+        return virtio_split_should_notify(vdev, vq);
> >+    }
> >+}
> >+
> >  void virtio_notify_irqfd(VirtIODevice *vdev, VirtQueue *vq)
> >  {
> >      bool should_notify;
>
Jason Wang Oct. 15, 2018, 9:11 a.m. UTC | #4 
On 2018年10月15日 16:20, Wei Xu wrote:
>>> +static void virtio_queue_set_notification_packed(VirtQueue *vq, int enable)
>>> +{
>>> +    VRingPackedDescEvent e;
>>> +    VRingMemoryRegionCaches *caches;
>>> +
>>> +    rcu_read_lock();
>>> +    caches  = vring_get_region_caches(vq);
>>> +    vring_packed_event_read(vq->vdev, &caches->device, &e);
>>> +
>>> +    if (!enable) {
>>> +        e.flags = RING_EVENT_FLAGS_DISABLE;
>>> +        goto out;
>>> +    }
>>> +
>>> +    e.flags = RING_EVENT_FLAGS_ENABLE;
>>> +    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
>>> +        uint16_t off_wrap = vq->event_idx | vq->event_wrap_counter << 15;
>> Btw, why not just use shadow_avail_idx here?
> It is nice to do that but an issue here is that it is 'shadow_avail_idx' for
> Rx but 'used_idx' for Tx when setting up for a kick, haven't figured out a
> clear fix because it helps easier migration part work, any idea?
>
> Wei
>

I'm not sure I get the point here. Why need to care about used_idx when 
enabling guest kick?

Thanks
diff mbox series

Patch

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index d12a7e3..1d25776 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -241,6 +241,30 @@  static void vring_desc_read(VirtIODevice *vdev, VRingDesc *desc,
     virtio_tswap16s(vdev, &desc->next);
 }
 
+static void vring_packed_event_read(VirtIODevice *vdev,
+                            MemoryRegionCache *cache, VRingPackedDescEvent *e)
+{
+    address_space_read_cached(cache, 0, e, sizeof(*e));
+    virtio_tswap16s(vdev, &e->off_wrap);
+    virtio_tswap16s(vdev, &e->flags);
+}
+
+static void vring_packed_off_wrap_write(VirtIODevice *vdev,
+                            MemoryRegionCache *cache, uint16_t off_wrap)
+{
+    virtio_tswap16s(vdev, &off_wrap);
+    address_space_write_cached(cache, 0, &off_wrap, sizeof(off_wrap));
+    address_space_cache_invalidate(cache, 0, sizeof(off_wrap));
+}
+
+static void vring_packed_flags_write(VirtIODevice *vdev,
+                            MemoryRegionCache *cache, uint16_t flags)
+{
+    virtio_tswap16s(vdev, &flags);
+    address_space_write_cached(cache, sizeof(uint16_t), &flags, sizeof(flags));
+    address_space_cache_invalidate(cache, sizeof(uint16_t), sizeof(flags));
+}
+
 static VRingMemoryRegionCaches *vring_get_region_caches(struct VirtQueue *vq)
 {
     VRingMemoryRegionCaches *caches = atomic_rcu_read(&vq->vring.caches);
@@ -347,7 +371,7 @@  static inline void vring_set_avail_event(VirtQueue *vq, uint16_t val)
     address_space_cache_invalidate(&caches->used, pa, sizeof(val));
 }
 
-void virtio_queue_set_notification(VirtQueue *vq, int enable)
+static void virtio_queue_set_notification_split(VirtQueue *vq, int enable)
 {
     vq->notification = enable;
 
@@ -370,6 +394,51 @@  void virtio_queue_set_notification(VirtQueue *vq, int enable)
     rcu_read_unlock();
 }
 
+static void virtio_queue_set_notification_packed(VirtQueue *vq, int enable)
+{
+    VRingPackedDescEvent e;
+    VRingMemoryRegionCaches *caches;
+
+    rcu_read_lock();
+    caches  = vring_get_region_caches(vq);
+    vring_packed_event_read(vq->vdev, &caches->device, &e);
+
+    if (!enable) {
+        e.flags = RING_EVENT_FLAGS_DISABLE;
+        goto out;
+    }
+
+    e.flags = RING_EVENT_FLAGS_ENABLE;
+    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
+        uint16_t off_wrap = vq->event_idx | vq->event_wrap_counter << 15;
+
+        vring_packed_off_wrap_write(vq->vdev, &caches->device, off_wrap);
+        /* Make sure off_wrap is wrote before flags */
+        smp_wmb();
+
+        e.flags = RING_EVENT_FLAGS_DESC;
+    }
+
+out:
+    vring_packed_flags_write(vq->vdev, &caches->device, e.flags);
+    rcu_read_unlock();
+}
+
+void virtio_queue_set_notification(VirtQueue *vq, int enable)
+{
+    vq->notification = enable;
+
+    if (!vq->vring.desc) {
+        return;
+    }
+
+    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
+        virtio_queue_set_notification_packed(vq, enable);
+    } else {
+        virtio_queue_set_notification_split(vq, enable);
+    }
+}
+
 int virtio_queue_ready(VirtQueue *vq)
 {
     return vq->vring.avail != 0;
@@ -2103,8 +2172,7 @@  static void virtio_set_isr(VirtIODevice *vdev, int value)
     }
 }
 
-/* Called within rcu_read_lock().  */
-static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
+static bool virtio_split_should_notify(VirtIODevice *vdev, VirtQueue *vq)
 {
     uint16_t old, new;
     bool v;
@@ -2127,6 +2195,58 @@  static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
     return !v || vring_need_event(vring_get_used_event(vq), new, old);
 }
 
+static bool vring_packed_need_event(VirtQueue *vq, uint16_t off_wrap,
+                                    uint16_t new, uint16_t old)
+{
+    bool wrap = vq->event_wrap_counter;
+    int off = off_wrap & ~(1 << 15);
+
+    if (new < old) {
+        new += vq->vring.num;
+        wrap ^= 1;
+    }
+
+    if (wrap != off_wrap >> 15) {
+        off += vq->vring.num;
+    }
+
+    return vring_need_event(off, new, old);
+}
+
+static bool virtio_packed_should_notify(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VRingPackedDescEvent e;
+    uint16_t old, new;
+    bool v;
+    VRingMemoryRegionCaches *caches;
+
+    caches  = vring_get_region_caches(vq);
+    vring_packed_event_read(vdev, &caches->driver, &e);
+
+    old = vq->signalled_used;
+    new = vq->signalled_used = vq->used_idx;
+    v = vq->signalled_used_valid;
+    vq->signalled_used_valid = true;
+
+    if (e.flags == RING_EVENT_FLAGS_DISABLE) {
+        return false;
+    } else if (e.flags == RING_EVENT_FLAGS_ENABLE) {
+        return true;
+    }
+
+    return !v || vring_packed_need_event(vq, e.off_wrap, new, old);
+}
+
+/* Called within rcu_read_lock().  */
+static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
+{
+    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
+        return virtio_packed_should_notify(vdev, vq);
+    } else {
+        return virtio_split_should_notify(vdev, vq);
+    }
+}
+
 void virtio_notify_irqfd(VirtIODevice *vdev, VirtQueue *vq)
 {
     bool should_notify;