On Tue, Oct 28, 2014 at 02:13:02AM +0000, Bin Wu wrote:
> The event idx in virtio is an effective way to reduce the number of
> interrupts and exits of the guest. When the guest puts an request
> into the virtio ring, it doesn't exit immediately to inform the
> backend. Instead, the guest checks the "avail" event idx to determine
> the notification.
>
> In virtqueue_pop, when a request is poped, the current avail event
> idx should be set to the number of vq->last_avail_idx.
>
> Signed-off-by: Bin Wu <[email protected]>
Does this fix some observable bug? Improve efficiency for some workload?
> ---
> hw/virtio/virtio.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 2c236bf..013979a 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -469,7 +469,7 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem)
>
> i = head = virtqueue_get_head(vq, vq->last_avail_idx++);
> if (vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) {
> - vring_avail_event(vq, vring_avail_idx(vq));
> + vring_avail_event(vq, vq->last_avail_idx);
> }
>
> if (vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_INDIRECT) {
> --
> 1.7.12.4
