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    Subject[RFC PATCH net-next 6/6] virtio-net: enable tx interrupt only for the final skb in the chain
    Date
    With the help of xmit_more and virtqueue_enable_cb_avail(), this patch
    enable tx interrupt only for the final skb in the chain if
    needed. This will help to mitigate tx interrupts.

    Cc: Rusty Russell <rusty@rustcorp.com.au>
    Cc: Michael S. Tsirkin <mst@redhat.com>
    Signed-off-by: Jason Wang <jasowang@redhat.com>
    ---
    drivers/net/virtio_net.c | 10 +++++++---
    1 files changed, 7 insertions(+), 3 deletions(-)

    diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
    index 2afc2e2..5943f3f 100644
    --- a/drivers/net/virtio_net.c
    +++ b/drivers/net/virtio_net.c
    @@ -993,12 +993,16 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
    virtqueue_disable_cb(sq->vq);
    }
    }
    - } else if (virtqueue_enable_cb(sq->vq)) {
    - free_old_xmit_skbs(sq, qsize);
    }

    - if (__netif_subqueue_stopped(dev, qnum) || !skb->xmit_more)
    + if (__netif_subqueue_stopped(dev, qnum) || !skb->xmit_more) {
    virtqueue_kick(sq->vq);
    + if (sq->vq->num_free >= 2 +MAX_SKB_FRAGS &&
    + unlikely(virtqueue_enable_cb_avail(sq->vq))) {
    + free_old_xmit_skbs(sq, qsize);
    + virtqueue_disable_cb(sq->vq);
    + }
    + }

    return NETDEV_TX_OK;
    }
    --
    1.7.1


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