On Wed, 17 Aug 2022 21:57:17 +0800, Guo Zhi <qtxuning1999 at sjtu.edu.cn>
wrote:> If in order feature negotiated, we can skip the used ring to get
> buffer's desc id sequentially.
>
> Signed-off-by: Guo Zhi <qtxuning1999 at sjtu.edu.cn>
> ---
> drivers/virtio/virtio_ring.c | 53 ++++++++++++++++++++++++++++++------
> 1 file changed, 45 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 1c1b3fa376a2..143184ebb5a1 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -144,6 +144,9 @@ struct vring_virtqueue {
> /* DMA address and size information */
> dma_addr_t queue_dma_addr;
> size_t queue_size_in_bytes;
> +
> + /* In order feature batch begin here */
> + u16 next_desc_begin;
> } split;
>
> /* Available for packed ring */
> @@ -702,8 +705,13 @@ static void detach_buf_split(struct vring_virtqueue
*vq, unsigned int head,
> }
>
> vring_unmap_one_split(vq, i);
> - vq->split.desc_extra[i].next = vq->free_head;
> - vq->free_head = head;
> + /* In order feature use desc in order,
> + * that means, the next desc will always be free
> + */
> + if (!virtio_has_feature(vq->vq.vdev, VIRTIO_F_IN_ORDER)) {
Call virtio_has_feature() here is not good.
Thanks.
> + vq->split.desc_extra[i].next = vq->free_head;
> + vq->free_head = head;
> + }
>
> /* Plus final descriptor */
> vq->vq.num_free++;
> @@ -745,7 +753,7 @@ static void *virtqueue_get_buf_ctx_split(struct
virtqueue *_vq,
> {
> struct vring_virtqueue *vq = to_vvq(_vq);
> void *ret;
> - unsigned int i;
> + unsigned int i, j;
> u16 last_used;
>
> START_USE(vq);
> @@ -764,11 +772,38 @@ static void *virtqueue_get_buf_ctx_split(struct
virtqueue *_vq,
> /* Only get used array entries after they have been exposed by host. */
> virtio_rmb(vq->weak_barriers);
>
> - last_used = (vq->last_used_idx & (vq->split.vring.num - 1));
> - i = virtio32_to_cpu(_vq->vdev,
> - vq->split.vring.used->ring[last_used].id);
> - *len = virtio32_to_cpu(_vq->vdev,
> - vq->split.vring.used->ring[last_used].len);
> + if (virtio_has_feature(_vq->vdev, VIRTIO_F_IN_ORDER)) {
> + /* Skip used ring and get used desc in order*/
> + i = vq->split.next_desc_begin;
> + j = i;
> + /* Indirect only takes one descriptor in descriptor table */
> + while (!vq->indirect && (vq->split.desc_extra[j].flags
& VRING_DESC_F_NEXT))
> + j = (j + 1) % vq->split.vring.num;
> + /* move to next */
> + j = (j + 1) % vq->split.vring.num;
> + /* Next buffer will use this descriptor in order */
> + vq->split.next_desc_begin = j;
> + if (!vq->indirect) {
> + *len = vq->split.desc_extra[i].len;
> + } else {
> + struct vring_desc *indir_desc > +
vq->split.desc_state[i].indir_desc;
> + u32 indir_num = vq->split.desc_extra[i].len, buffer_len = 0;
> +
> + if (indir_desc) {
> + for (j = 0; j < indir_num / sizeof(struct vring_desc); j++)
> + buffer_len += indir_desc[j].len;
> + }
> +
> + *len = buffer_len;
> + }
> + } else {
> + last_used = (vq->last_used_idx & (vq->split.vring.num - 1));
> + i = virtio32_to_cpu(_vq->vdev,
> + vq->split.vring.used->ring[last_used].id);
> + *len = virtio32_to_cpu(_vq->vdev,
> + vq->split.vring.used->ring[last_used].len);
> + }
>
> if (unlikely(i >= vq->split.vring.num)) {
> BAD_RING(vq, "id %u out of range\n", i);
> @@ -2236,6 +2271,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int
index,
> vq->split.avail_flags_shadow = 0;
> vq->split.avail_idx_shadow = 0;
>
> + vq->split.next_desc_begin = 0;
> +
> /* No callback? Tell other side not to bother us. */
> if (!callback) {
> vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
> --
> 2.17.1
>