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

[Jens Freimann]

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.

s/bathing/batching/


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];

I think code is safe as it is, but should we check if cookie actually points to 
something?

I tested this patch and saw the same performance improvement, so

Tested-by: Jens Freimann <jfreim...@redhat.com>
Reviewed-by: Jens Freimann <jfreim...@redhat.com>

regards,
Jens