vhost: support virtqueue interrupt/notification suppression

The driver can suppress interrupt when VIRTIO_F_EVENT_IDX feature bit is
negotiated. The driver set vring flags to 0, and MAY use used_event in
available ring to advise device interrupt util reach an index specified
by used_event. The device ignore the lower bit of vring flags, and send
an interrupt when index reach used_event.

The device can suppress notification in a manner analogous to the ways
driver suppress interrupt. The device manipulates flags or avail_event in
the used ring in the same way the driver manipulates flags or used_event in
available ring.

Signed-off-by: Junjie Chen <junjie.j.chen@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Tested-by: Lei Yao <lei.a.yao@intel.com>
Acked-by: Yuanhan Liu <yliu@fridaylinux.org>

diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
index 5cc7cad..6789ccc 100644 (file)
--- a/lib/librte_vhost/vhost.c
+++ b/lib/librte_vhost/vhost.c
@@ -509,7 +509,7 @@ rte_vhost_vring_call(int vid, uint16_t vring_idx)
        if (!vq)
                return -1;
 
-       vhost_vring_call(vq);
+       vhost_vring_call(dev, vq);
        return 0;
 }
 

diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 487aedd..f9cc7e6 100644 (file)
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -74,6 +74,8 @@ struct vhost_virtqueue {
 
        uint16_t                last_avail_idx;
        uint16_t                last_used_idx;
+       /* Last used index we notify to front end. */
+       uint16_t                signalled_used;
 #define VIRTIO_INVALID_EVENTFD         (-1)
 #define VIRTIO_UNINITIALIZED_EVENTFD   (-2)
 
@@ -185,6 +187,7 @@ struct vhost_msg {
                                (1ULL << VIRTIO_NET_F_GUEST_TSO6) | \
                                (1ULL << VIRTIO_NET_F_GUEST_UFO) | \
                                (1ULL << VIRTIO_RING_F_INDIRECT_DESC) | \
+                               (1ULL << VIRTIO_RING_F_EVENT_IDX) | \
                                (1ULL << VIRTIO_NET_F_MTU) | \
                                (1ULL << VIRTIO_F_IOMMU_PLATFORM))
 
@@ -370,16 +373,47 @@ vhost_iova_to_vva(struct virtio_net *dev, struct vhost_virtqueue *vq,
        return __vhost_iova_to_vva(dev, vq, iova, size, perm);
 }
 
+#define vhost_used_event(vr) \
+       (*(volatile uint16_t*)&(vr)->avail->ring[(vr)->size])
+
+/*
+ * The following is used with VIRTIO_RING_F_EVENT_IDX.
+ * Assuming a given event_idx value from the other size, if we have
+ * just incremented index from old to new_idx, should we trigger an
+ * event?
+ */
+static __rte_always_inline int
+vhost_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
+{
+       return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
+}
+
 static __rte_always_inline void
-vhost_vring_call(struct vhost_virtqueue *vq)
+vhost_vring_call(struct virtio_net *dev, struct vhost_virtqueue *vq)
 {
        /* Flush used->idx update before we read avail->flags. */
        rte_mb();
 
-       /* Kick the guest if necessary. */
-       if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
-                       && (vq->callfd >= 0))
-               eventfd_write(vq->callfd, (eventfd_t)1);
+       /* Don't kick guest if we don't reach index specified by guest. */
+       if (dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX)) {
+               uint16_t old = vq->signalled_used;
+               uint16_t new = vq->last_used_idx;
+
+               LOG_DEBUG(VHOST_DATA, "%s: used_event_idx=%d, old=%d, new=%d\n",
+                       __func__,
+                       vhost_used_event(vq),
+                       old, new);
+               if (vhost_need_event(vhost_used_event(vq), new, old)
+                       && (vq->callfd >= 0)) {
+                       vq->signalled_used = vq->last_used_idx;
+                       eventfd_write(vq->callfd, (eventfd_t) 1);
+               }
+       } else {
+               /* Kick the guest if necessary. */
+               if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
+                               && (vq->callfd >= 0))
+                       eventfd_write(vq->callfd, (eventfd_t)1);
+       }
 }
 
 #endif /* _VHOST_NET_CDEV_H_ */

diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index cd304f6..68bafd9 100644 (file)
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -384,7 +384,7 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
                offsetof(struct vring_used, idx),
                sizeof(vq->used->idx));
 
-       vhost_vring_call(vq);
+       vhost_vring_call(dev, vq);
 out:
        if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
                vhost_user_iotlb_rd_unlock(vq);
@@ -671,7 +671,7 @@ virtio_dev_merge_rx(struct virtio_net *dev, uint16_t queue_id,
 
        if (likely(vq->shadow_used_idx)) {
                flush_shadow_used_ring(dev, vq);
-               vhost_vring_call(vq);
+               vhost_vring_call(dev, vq);
        }
 
 out:
@@ -1075,7 +1075,7 @@ update_used_idx(struct virtio_net *dev, struct vhost_virtqueue *vq,
        vq->used->idx += count;
        vhost_log_used_vring(dev, vq, offsetof(struct vring_used, idx),
                        sizeof(vq->used->idx));
-       vhost_vring_call(vq);
+       vhost_vring_call(dev, vq);
 }
 
 static __rte_always_inline struct zcopy_mbuf *