On Wed, Aug 17, 2022 at 3:58 PM Guo Zhi <qtxuning1999@xxxxxxxxxxx> wrote:
>
> Follow VIRTIO 1.1 spec, only writing out a single used ring for a batch
> of descriptors.
>
> Signed-off-by: Guo Zhi <qtxuning1999@xxxxxxxxxxx>
> ---
> drivers/vhost/vhost.c | 14 ++++++++++++--
> drivers/vhost/vhost.h | 1 +
> 2 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 40097826cff0..7b20fa5a46c3 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2376,10 +2376,20 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
> vring_used_elem_t __user *used;
> u16 old, new;
> int start;
> + int copy_n = count;
>
> + /**
> + * If in order feature negotiated, devices can notify the use of a batch of buffers to
> + * the driver by only writing out a single used ring entry with the id corresponding
> + * to the head entry of the descriptor chain describing the last buffer in the batch.
> + */
> + if (vhost_has_feature(vq, VIRTIO_F_IN_ORDER)) {
> + copy_n = 1;
> + heads = &heads[count - 1];
> + }
> start = vq->last_used_idx & (vq->num - 1);
> used = vq->used->ring + start;
> - if (vhost_put_used(vq, heads, start, count)) {
> + if (vhost_put_used(vq, heads, start, copy_n)) {
> vq_err(vq, "Failed to write used");
> return -EFAULT;
> }
> @@ -2410,7 +2420,7 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
>
> start = vq->last_used_idx & (vq->num - 1);
> n = vq->num - start;
> - if (n < count) {
> + if (n < count && !vhost_has_feature(vq, VIRTIO_F_IN_ORDER)) {
> r = __vhost_add_used_n(vq, heads, n);
> if (r < 0)
> return r;
It would be simpler to use vhost_add_used in vsock/vhost_test to add a
batch of used descriptors, and leave vhost_add_used_n untouched.
Since it's the upper layer the one that manages the in_order in this
version, we could:
* Always call vhost_add_used(vq, last_head_of_batch, ...) for the tx
queue, that does not need used length info.
* Call vhost_add_used_n for the rx queue, since the driver needs the
used length info.
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index d9109107af08..0d5c49a30421 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -236,6 +236,7 @@ enum {
> VHOST_FEATURES = (1ULL << VIRTIO_F_NOTIFY_ON_EMPTY) |
> (1ULL << VIRTIO_RING_F_INDIRECT_DESC) |
> (1ULL << VIRTIO_RING_F_EVENT_IDX) |
> + (1ULL << VIRTIO_F_IN_ORDER) |
> (1ULL << VHOST_F_LOG_ALL) |
> (1ULL << VIRTIO_F_ANY_LAYOUT) |
> (1ULL << VIRTIO_F_VERSION_1)
> --
> 2.17.1
>
