Re: [dpdk-dev] [PATCH v2 3/3] net/virtio: improve batching in mergeable path

[Maxime Coquelin]

On 12/19/18 12:18 PM, Tiwei Bie wrote:

On Tue, Dec 11, 2018 at 02:48:04PM +0100, Maxime Coquelin wrote:

This patch improves both descriptors dequeue and refill,
by using the same bathing strategy as done in in-order path.

Signed-off-by: Maxime Coquelin <maxime.coque...@redhat.com>
---
  drivers/net/virtio/virtio_rxtx.c | 237 ++++++++++++++++---------------
  1 file changed, 126 insertions(+), 111 deletions(-)

diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
index ebe5c74b5..59bcac2f7 100644
--- a/drivers/net/virtio/virtio_rxtx.c
+++ b/drivers/net/virtio/virtio_rxtx.c
@@ -267,41 +267,42 @@ virtqueue_enqueue_refill_inorder(struct virtqueue *vq,
  }

static inline int

-virtqueue_enqueue_recv_refill(struct virtqueue *vq, struct rte_mbuf *cookie)
+virtqueue_enqueue_recv_refill(struct virtqueue *vq, struct rte_mbuf **cookie,
+                               uint16_t num)
  {
        struct vq_desc_extra *dxp;
        struct virtio_hw *hw = vq->hw;
-       struct vring_desc *start_dp;
-       uint16_t needed = 1;
-       uint16_t head_idx, idx;
+       struct vring_desc *start_dp = vq->vq_ring.desc;
+       uint16_t idx, i;

if (unlikely(vq->vq_free_cnt == 0))

                return -ENOSPC;
-       if (unlikely(vq->vq_free_cnt < needed))
+       if (unlikely(vq->vq_free_cnt < num))
                return -EMSGSIZE;

- head_idx = vq->vq_desc_head_idx;

-       if (unlikely(head_idx >= vq->vq_nentries))
+       if (unlikely(vq->vq_desc_head_idx >= vq->vq_nentries))
                return -EFAULT;

- idx = head_idx;

-       dxp = &vq->vq_descx[idx];
-       dxp->cookie = (void *)cookie;
-       dxp->ndescs = needed;
+       for (i = 0; i < num; i++) {
+               idx = vq->vq_desc_head_idx;
+               dxp = &vq->vq_descx[idx];
+               dxp->cookie = (void *)cookie[i];
+               dxp->ndescs = 1;

- start_dp = vq->vq_ring.desc;

-       start_dp[idx].addr =
-               VIRTIO_MBUF_ADDR(cookie, vq) +
-               RTE_PKTMBUF_HEADROOM - hw->vtnet_hdr_size;
-       start_dp[idx].len =
-               cookie->buf_len - RTE_PKTMBUF_HEADROOM + hw->vtnet_hdr_size;
-       start_dp[idx].flags =  VRING_DESC_F_WRITE;
-       idx = start_dp[idx].next;
-       vq->vq_desc_head_idx = idx;
-       if (vq->vq_desc_head_idx == VQ_RING_DESC_CHAIN_END)
-               vq->vq_desc_tail_idx = idx;
-       vq->vq_free_cnt = (uint16_t)(vq->vq_free_cnt - needed);
-       vq_update_avail_ring(vq, head_idx);
+               start_dp[idx].addr =
+                       VIRTIO_MBUF_ADDR(cookie[i], vq) +
+                       RTE_PKTMBUF_HEADROOM - hw->vtnet_hdr_size;
+               start_dp[idx].len =
+                       cookie[i]->buf_len - RTE_PKTMBUF_HEADROOM +
+                       hw->vtnet_hdr_size;
+               start_dp[idx].flags = VRING_DESC_F_WRITE;
+               vq->vq_desc_head_idx = start_dp[idx].next;
+               if (vq->vq_desc_head_idx == VQ_RING_DESC_CHAIN_END)
+                       vq->vq_desc_tail_idx = vq->vq_desc_head_idx;

It's better to break the loop here. Or maybe move
this check out of the loop.

Right, I vote for breaking, else we might get an out of bound access.

Thanks!

+               vq_update_avail_ring(vq, idx);
+       }
+
+       vq->vq_free_cnt = (uint16_t)(vq->vq_free_cnt - num);

return 0;

  }

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