From: David Ahern <d...@cumulusnetworks.com>
Date: Tue, 25 Aug 2015 15:37:55 -0700
> On 8/25/15 2:02 PM, David Miller wrote:
>> From: David Ahern <d...@cumulusnetworks.com>
>> Date: Sun, 23 Aug 2015 12:41:00 -0600
>>
>>> @@ -250,6 +253,17 @@ static netdev_tx_t vrf_xmit(struct sk_buff *skb,
>>> struct net_device *dev)
>>>
>>> static netdev_tx_t vrf_finish(struct sock *sk, struct sk_buff *skb)
>>> {
>>> + int err;
>>> +
>>> + __skb_pull(skb, skb_network_offset(skb));
>>> + err = dev_hard_header(skb, skb->dev, ntohs(skb->protocol),
>>> + NULL, NULL, skb->len);
>>> +
>>> + if (err < 0) {
>>> + vrf_tx_error(skb->dev, skb);
>>> + return -EINVAL;
>>> + }
>>> +
>>> return dev_queue_xmit(skb);
>>
>> This is expensive and rediculous to do for every TX frame.
>>
>> You'll need to find another way.
>>
>
> The packet is directed here from the IP layer via the custom dst, so
> there is no L2 header on the skb. So while the push and pop of the
> header seems silly it is part and parcel of the feature to run tcpdump
> on the VRF device. I don't see how it could be done any other way.
You're losing a significant optimization on the transmit path by not
using the neighbour table entry hard header cache.
That's what I want you to fix.
See dst_neigh_output() and in particular neigh_hh_output().
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