On Wed, May 04, 2011 at 04:58:18PM -0500, Tom Lendacky wrote:
>
> On Wednesday, May 04, 2011 03:51:47 PM Michael S. Tsirkin wrote:
> > Use the new avail_event feature to reduce the number
> > of exits from the guest.
> >
> > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > ---
> > drivers/virtio/virtio_ring.c | 39
> > ++++++++++++++++++++++++++++++++++++++- 1 files changed, 38 insertions(+),
> > 1 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 3a3ed75..262dfe6 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -82,6 +82,15 @@ struct vring_virtqueue
> > /* Host supports indirect buffers */
> > bool indirect;
> >
> > + /* Host publishes avail event idx */
> > + bool event;
> > +
> > + /* Is kicked_avail below valid? */
> > + bool kicked_avail_valid;
> > +
> > + /* avail idx value we already kicked. */
> > + u16 kicked_avail;
> > +
> > /* Number of free buffers */
> > unsigned int num_free;
> > /* Head of free buffer list. */
> > @@ -228,6 +237,12 @@ add_head:
> > * new available array entries. */
> > virtio_wmb();
> > vq->vring.avail->idx++;
> > + /* If the driver never bothers to kick in a very long while,
> > + * avail index might wrap around. If that happens, invalidate
> > + * kicked_avail index we stored. TODO: make sure all drivers
> > + * kick at least once in 2^16 and remove this. */
> > + if (unlikely(vq->vring.avail->idx == vq->kicked_avail))
> > + vq->kicked_avail_valid = true;
>
> vq->kicked_avail_valid should be set to false here.
>
> Tom
Right, good catch.
> >
> > pr_debug("Added buffer head %i to %p\n", head, vq);
> > END_USE(vq);
> > @@ -236,6 +251,23 @@ add_head:
> > }
> > EXPORT_SYMBOL_GPL(virtqueue_add_buf_gfp);
> >
> > +
> > +static bool vring_notify(struct vring_virtqueue *vq)
> > +{
> > + u16 old, new;
> > + bool v;
> > + if (!vq->event)
> > + return !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY);
> > +
> > + v = vq->kicked_avail_valid;
> > + old = vq->kicked_avail;
> > + new = vq->kicked_avail = vq->vring.avail->idx;
> > + vq->kicked_avail_valid = true;
> > + if (unlikely(!v))
> > + return true;
> > + return vring_need_event(vring_avail_event(&vq->vring), new, old);
> > +}
> > +
> > void virtqueue_kick(struct virtqueue *_vq)
> > {
> > struct vring_virtqueue *vq = to_vvq(_vq);
> > @@ -244,7 +276,7 @@ void virtqueue_kick(struct virtqueue *_vq)
> > /* Need to update avail index before checking if we should notify */
> > virtio_mb();
> >
> > - if (!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
> > + if (vring_notify(vq))
> > /* Prod other side to tell it about changes. */
> > vq->notify(&vq->vq);
> >
> > @@ -437,6 +469,8 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
> > vq->vq.name = name;
> > vq->notify = notify;
> > vq->broken = false;
> > + vq->kicked_avail_valid = false;
> > + vq->kicked_avail = 0;
> > vq->last_used_idx = 0;
> > list_add_tail(&vq->vq.list, &vdev->vqs);
> > #ifdef DEBUG
> > @@ -444,6 +478,7 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
> > #endif
> >
> > vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC);
> > + vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_AVAIL_EVENT_IDX);
> >
> > /* No callback? Tell other side not to bother us. */
> > if (!callback)
> > @@ -482,6 +517,8 @@ void vring_transport_features(struct virtio_device
> > *vdev) break;
> > case VIRTIO_RING_F_USED_EVENT_IDX:
> > break;
> > + case VIRTIO_RING_F_AVAIL_EVENT_IDX:
> > + break;
> > default:
> > /* We don't understand this bit. */
> > clear_bit(i, vdev->features);
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