From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <dada1@cosmosbay.com>
Subject: Re: [PATCH] loopback: better handling of packet drops
Date: Fri, 17 Apr 2009 17:05:42 +0200
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Cc: David Miller <davem@davemloft.net>, netdev@vger.kernel.org
To: Stephen Hemminger <shemminger@vyatta.com>
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Stephen Hemminger a =C3=A9crit :
> On Fri, 17 Apr 2009 12:33:33 +0200
> Eric Dumazet <dada1@cosmosbay.com> wrote:
>>  static int loopback_xmit(struct sk_buff *skb, struct net_device *de=
v)
>>  {
>>  	struct pcpu_lstats *pcpu_lstats, *lb_stats;
>> +	int len;
>> =20
>>  	skb_orphan(skb);
>> =20
>> -	skb->protocol =3D eth_type_trans(skb,dev);
>> +	skb->protocol =3D eth_type_trans(skb, dev);
>> =20
>>  	/* it's OK to use per_cpu_ptr() because BHs are off */
>>  	pcpu_lstats =3D dev->ml_priv;
>>  	lb_stats =3D per_cpu_ptr(pcpu_lstats, smp_processor_id());
>> -	lb_stats->bytes +=3D skb->len;
>> -	lb_stats->packets++;
>> =20
>> -	netif_rx(skb);
>> +	len =3D skb->len;
>> +	if (likely(__netif_rx(skb) =3D=3D NET_RX_SUCCESS)) {
>> +		lb_stats->bytes +=3D len;
>> +		lb_stats->packets++;
>> +		return NETDEV_TX_OK;
>> +	}
>> +	lb_stats->drops++;
>> =20
>> -	return 0;
>> +	return NETDEV_TX_BUSY;
>>  }
>=20
> If you return NETDEV_TX_BUSY, then the xmit logic will retry
> so it is not really a drop but a stall. I think it is confusing
> to call this a packet loss.

Good point, thanks.
So we should not account this stall in dev stats ? Maybe in 'collisions=
' ?

I also discovered we had to do
skb_push(skb, ETH_HLEN); /* undo the skb_pull() done in eth_type_trans(=
) */
before returning NETDEV_TX_BUSY;