[RFC v2 6/7] virtio: in order support for virtio_ring

From: Guo Zhi
Date: Wed Aug 17 2022 - 09:59:50 EST


If in order feature negotiated, we can skip the used ring to get
buffer's desc id sequentially.

Signed-off-by: Guo Zhi <qtxuning1999@xxxxxxxxxxx>
---
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)) {
+ 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