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
>
> 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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