Subject: Re: [PATCH] netdev: pktgen xmit packet through vlan interface

From: John Fastabend <[email-masked]>
Date: Fri, 02 May 2014 07:00:00 -0700

On 5/2/2014 6:19 AM, Jesper Dangaard Brouer wrote:
> On Fri,  2 May 2014 15:18:12 +0800
> Zhouyi Zhou <[email-masked]> wrote:
>
>> As http://www.spinics.net/lists/netdev/msg165015.html
>> pktgen generates shared packet through vlan interface will cause
>> oops because of duplicate entering tc queue.
>>
>> Try to solve this problem by means of packet clone instead of sharing.
>
> I really don't like adding this stuff to the fast path of pktgen.
>
> Why would you use pktgen on a VLAN?

Its a good way to test qdiscs. When you run pktgen over the VLAN
you exercise the lower devices qdisc.

Although I never submitted a patch like this because I figured it
was a corner case and we would want to keep the hotpath clean.

>
> Why don't you use the "vlan_id" feature available in pktgen, and send
> in the lower real device?
>
>
>
>> Signed-off-by: Zhouyi Zhou <[email-masked]>
>> ---
>>   net/core/pktgen.c |   20 +++++++++++++++++---
>>   1 files changed, 17 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
>> index 0304f98..ced07fc 100644
>> --- a/net/core/pktgen.c
>> +++ b/net/core/pktgen.c
>> @@ -3297,6 +3297,7 @@ static void pktgen_xmit(struct pktgen_dev *pkt_dev)
>>   	netdev_tx_t (*xmit)(struct sk_buff *, struct net_device *)
>>   		= odev->netdev_ops->ndo_start_xmit;
>>   	struct netdev_queue *txq;
>> +	struct sk_buff *nskb = NULL;
>>   	u16 queue_map;
>>   	int ret;
>>
>> @@ -3347,8 +3348,18 @@ static void pktgen_xmit(struct pktgen_dev *pkt_dev)
>>   		pkt_dev->last_ok = 0;
>>   		goto unlock;
>>   	}
>> -	atomic_inc(&(pkt_dev->skb->users));
>> -	ret = (*xmit)(pkt_dev->skb, odev);
>> +
>> +	if (pkt_dev->clone_skb && is_vlan_dev(odev)) {
>> +		nskb = skb_clone(pkt_dev->skb, GFP_ATOMIC);
>> +		ret = -ENOMEM;
>> +		if (nskb)
>> +			ret = (*xmit)(nskb, odev);
>> +		else
>> +			nskb = ERR_PTR(ret);
>> +	} else {
>> +		atomic_inc(&(pkt_dev->skb->users));
>> +		ret = (*xmit)(pkt_dev->skb, odev);
>> +	}
>>
>>   	switch (ret) {
>>   	case NETDEV_TX_OK:
>> @@ -3372,7 +3383,10 @@ static void pktgen_xmit(struct pktgen_dev *pkt_dev)
>>   	case NETDEV_TX_LOCKED:
>>   	case NETDEV_TX_BUSY:
>>   		/* Retry it next time */
>> -		atomic_dec(&(pkt_dev->skb->users));
>> +		if (nskb && !IS_ERR(nskb))
>> +			kfree_skb(nskb);
>> +		else
>> +			atomic_dec(&(pkt_dev->skb->users));
>>   		pkt_dev->last_ok = 0;
>>   	}
>>   unlock:
>
>
>